6 man would be fine. However, I think 8 man would be better as it could be made more so to require the trinity.
The way combat is designed in this game it is easier to avoid needing a healer for small group content. With 6 man it would likely be that it can be done without a healer or with only a 50/50 healer.
The only way to avoid that scenarios it to use unavoidable heavy damage which goes against much of the design of this game. IMHO. Zos has put in some heavy damage that hits the tank but in most cases it can just be dodged and avoided completely.
I am unsure about the details, but I would be well up for 6 man content. Definitely support.
A bit off topic, feel free to skip:
To be honest, I think the entire balance of the difficulty progression viz dungeons/trials, could do with a rework.
We have normal & vet dungeons non dlc. Normal dlc & vet dlc. There is a variety of difficulty and a large skill cap difference between normal and vet throughout. Then of course the trials, with +2 versions & vet etc.
It works, and I love it, but it is all a bit of a mish mash, particularly for newer players who are the life blood of ESO, we need them. A rework of the mechanics, adds, bosses, difficulties etc, could provide a clearer, more defined, more gradual transition through skill cap, gear, experience progression etc.
6 man dungeons/trials could play a major role in this. Also allowing folk to access better trial type gear, which is often unreachable for the average player.