One of the interesting things I've seen discussed about tanks and healers is that when you want to get serious it kind of sucks to be a healer/tank, I mean you do get that sweet queue time for normal content but when it's to true end game content (savage, other highly group focused content) you're part of a select small group and that makes it bit of an issue to want to always maintain a strong tank when DD is a much larger wanted group. It basically becomes a wall of interest, you gear up and go quickly until all a sudden you're not desired at all and you need to go focus on something else instead. If a tank spot does open up it might be good, but that would happen far less often and since tanks seem to get to be leader of the content (at least in my WoW experience and the people I've talked to in FFXIV's experience, suggest they really don't like having tanks to cycle and want a fixed one).
Of course if you never do end content it's probably never going to appear to be an issue (fast queues times is your reward lol).
So just something I wanted to see what people thought about, is what if there is at least one or two jobs that broke the mold in gearing up - which would mean that for example a healer could be gearing out their DD /and/ their Healer at the same time (or tank). Leading to a few benefits, both in mold breaking (can be refreshing change of pace), and interlinking progress between two roles increasing movement between those two roles.
So if your group doesn't need another tank, you go DD no problem, if they need a tank omg there are three people who can be one (or healer).
Blue mage (tank) for example could be using some DD mage gear (or fill in whatever other light weight class). DD gear used for a specific tank job.
Dancer (healer) could use monk gear (I mean the monk on the SB trailer made everyone think it was a dancer, so pretty close already eh? add some good artifact armor just in case though lol). DD gear used for a specific healer job.
It can of course go the other direction - and this would make the move more general/easier for tanks and healers, like some may be familiar with Golbez who is a big hulking super mage - so you could make a new mage type and give it tank armor. Perhaps because we already have a BLM (which Golbez matches fairly closely to) instead you make a magitek / judge damage dealing job which wears heavy armor but is still actually a DD. Tank gear used for a specific DD job.
Golbez:
Inspiration for a new job/gunblade/soldier/magitek/judge DD that uses tank gear:
(yeah I know who that is lol)
Perhaps Geomancer uses healer robes but is actually DD. Healer gear used for a specific DD job. (Thought Geomancer since WHM has access to those elements and is healer, so there could be some lore/story referencing each other and WHM's gate into pure war or something.)
Now of course you could say what about gear with a tank healer relationship, which might be fun but I think part of the big bonus in the idea of breaking the mold is that you are gearing the large pool class (DD) when you gear the small pool class (healer/tank)... So gearing two small pools misses that benefit, but I'm not suggesting some people wouldn't find that interesting.
You could begin to argue that "what if tanks/healers could just queue as a DD instead" which may work, a special stance that locks you into a damage spec and your spells change a bit - but I think it adds more balance challenge than just making an extra job that breaks the equipment mold. The other thing is if the job breaks the mold it means you might encourage players who started out DD actually try healer/tank because they love a job that shares gear that is in a different role. Of course for loot rules you'll want to adjust the drop rates according to who is there, but as we've already heard/read SE is changing how loot drops already so that shouldn't be much of an issue.
May encourage the jobs greatly for a time because of the gear sharing cross role feature but in the end I believe not everyone wants to be a tank/healer and so you'd just boost the number of people willing but you'd reach a ceiling cap at some point still. So it wouldn't kill other jobs because a few could share cross a role, although it is a thing to think about.
I don't think the issue is end of the world/has to be fixed or whatever, but I found that the issue is a thing that might demote being a healer/tank more than they already are and that you could approach the issue with a solution that not only allows healers and tanks to phase into DD with balance (new job that uses their gear/or other way around), but also could be an interesting breath of expectation in the game. As at the moment having a DD in an out of role gear is unexpected, or the other way around and seeing while Blue Mage fits Tank thematically (gets hit to become stronger/learn) it doesn't really fit as well in visuals with other tank gears without perhaps just extremely relying on artifact armor (so blue mage then becomes a good example of how you could have a tank in mage gear, of course others have used other examples as well for mage tanks).
tl;dr: a job that uses out of role gear that allows healers or tanks a transit into DD, encouraging transit between the roles and freedom for people who main stay healer/tank but are not needed in their current raid environment but would like to be later.