The 'get rid of alts/off specs' idea while absolutely terrible, is kind of why healers weren't losing spots in early era WoW. In the days of yore, you didn't have an offspec. You could respec, but you had to go back to town and spend a bunch of money to do it, and that cost only got bigger each time you did it. Gear didn't swap primary stat based on spec so you needed two completely different sets of gear, and of course with maybe a separate resistance set for your other spec, because resistance gear fights were a thing back then. Only the people hard core pushing content had people who routinely would swap specs. Swapping a spec back then was a big deal. If you swapped? You probably did for a longer term deal. Groups like ours didn't see much in the way of spec swapping, just the Death'n'Taxes top end groups.
This meant that a raid of 2 tanks, 3 healers and 5 DPS usually stayed at those numbers, even as you began to outgear the content. As Blizzard made having multiple specs easier? Those numbers got way more flexible and suddenly a tactic that really only super, super hardcore people could do, became very easy for even casual players to do. So now as content gets easier, you speed it up by flipping a healer to a DPS. ...which sucks if you like to heal since your spots dry up as you gear up.
I think this is actually the first expansion ever that has made a change that has made alts/off-specs more difficult than previous ones. The trend has been slowly moving towards making it easier to have multiple specs and characters, and this one they finally took it a big step in the other direction. Unfortunately how the game has been played has migrated to adjusting towards that flexibility and ease of off specs, so it's been a big shock. A lot of raids are run under the assumption you have some people who like and don't mind spec swapping. Honestly? I think that's all made the game better. It is so much easier to run a raid now between how easy it's been for people to maintain offspecs as well as the flex raid size thing. Issues that would sideline a day of raiding are now just a speed bump. Healer is sick? Have a DPS swap over. Someone can't make it? Run with 11 instead of 12. A friend really wants to play and is all geared and ready? Sweet, c'mon in. Run with 13 instead of 12. The amount of drama in a raid group seems far, far less than it was. (I mean, also...we were all a lot younger, stupider and more immature back then too)
The 'HEALERS ARE LOSING THEIR JERBS' problem is a tougher one. The creep in power over a raid makes it easier. Healers do more healing, tanks get tougher, and as DPS increases the fight shrinks and the raid needs less healing. You hit a point where you flip a healer to a DPS and make it even shorter to clear more content in less time. It's not just a mythic tactic as groups like ours have limited raiding time so going fast is important to make the most of our limited time. Gearing up is also important since as we're not mega top end, we need the gear to clear various fight hurdles. This really sucks if what you like to do in this game is heal. Not only will your job get flipped, but your job also gets more boring as fights get easier. DPS at least can try to beat their numbers, beat their times. DPS can treat it like a time trial, it's easy, but you can see if you can do a lap a little bit faster than last time. There's nothing healers can really do in that vein. They do less and less as the numbers go up.
Removing gear and the power creep isn't an option since gear helps groups progress and keeps raiding accessible to a wider range of skill levels. We're not good enough to clear a lot of fights out of the gate, but gear helps us overcome that. A top end mythic group could clear heroic with a fraction of the ilevel a lot of us need. ...but that ilevel creep is what lets us take on those challenges and get over various humps. Gear makes up for mistakes and makes the game more accessible at a variety of skill levels. Super good people can clear heroic nearly the first night it opens, and then there's a nice balance of people who clear it as they gear up based on ilvl and how much time they raid. If you're not as good, you can put in more time to learn things, and more time to gear up and you'll clear those hurdles in your own way. It's been satisfying and honestly it's a pretty good system. ...unless you like healing.
One thing they could try is a challenge mode raid. It's basically a challenge dungeon where when you enter, all your gear is normalized statwise so everyone is on the same level and there's no power creep. Going through a challenge mode raid you likely won't see as many healers being dropped since at no point is the healing going to get easier. (Maybe execution, people standing in shit less, but removing the safety net in this instance is a much bigger deal) They could make two tiers of challenge mode and even flip it so the top end challenge mode is the 'hardest' in the game and focus the PvE world firsts on challenge mode so gear isn't even a factor, it's just pure tactics. For some people this might even make raiding more accessible since there is far less prep work needed to get in on one. Again, for other groups it's not the right answer so others will need the power creep to clear hurdles, and there is something satisfying about your spec/rotation getting better and different via gear.
Another thing is just giving healers something else to do that isn't healing, but also isn't DPS. Find some other support style gameplay they can do that also increases over time and also helps a fight along so you want to keep healers in their healing spec. ...unfortunately the only thing I can think of is scaling buffs they throw at DPS that require some amount of finesse and/or timing to use right....which is basically a sideways way of "Healers do DPS when they don't heal"
I could maybe see fights being designed with mechanics that let you beat a fight quicker if you have monster healing numbers. Like...boss does terrible whirlwind of death. Ranged gotta run, melee gotta run out, but while in this mode boss takes 200% more damage. When your healers get buff enough? People can just stand through it and DPS...which shrinks the fight, but only if your healing is good enough. Creating tactics like this will allow raids to take on riskier strategies to speed stuff up, but rely on higher healing output to do it. Then there's always the 'heal the boss' style fights which healers sorta act as DPS. You can't do mechanics like this on EVERY fight, but I think boss design is a good way to incentivize bringing healers. Create more situations where you want to pump out monster healing numbers, and get creative on how you do it. Reward it.
Anyway, this had little to do with the artifact topic, but kinda followed on. Back to work!