The graphics and the complexity of the game aren't that much of a barrier to entry I don't think. There's a massive movement of newer indie games that have relatively poor graphics and are quite complicated but are really popular.
The trouble with UO is the cost of entry and lack of social media presence.
I recently resubscribed after a 10+ year break. I considered playing a bunch of times over the last few years, but whenever I got to the subscription screen I got annoyed by the fact it was still a tenner for a month. So anyway, this month I decided to bite the bullet and resubscribed. I played a little while before realising I probably need to buy a soulstone to adjust my old character templates. So down goes some more money. Then I realised I that imbuing would be really helpful to get my gear optimised, so I spend a bit more money on Stygian Abyss. Now I'm looking at the benefits of skill masteries. I'm thinking having access to them would make my characters more powerful, but I'm essentially dropping £15 just to be able to use them, as the rest of the expansion content isn't interesting to me.
I've got a job and I can afford this stuff, but I have a really acute sense that I'm being ripped off by EA/Broadsword. I have a strong sense of nostalgia driving my desire to come back and play, but a new player wouldn't have that and wouldn't put up with the blatant fleecing.
I think a really proactive development team that was in tune with the current gaming trends could really revitilise UO. There's a ton of good, re-playable content in it that would attract new players. The original client and graphics are absolutely fine and are just in need of a bit of optimisation.
Some suggestions as a new returner:
1. Optimise the old client to run a bit smoother/work better with higher res monitors
2. Condense a few of the shards to increase population (may do something like WoW with cross-server zones for dungeons etc)
3. Produce a starter pack/returner pack (something like all the expansion packs and a free 30 days for £20. Put a nice special mount or item in there as an ingame bonus)
4. Review the subscription cost (maybe reduce it by 30-50%) and add more content to the ingame store. Personally, if the sub cost was a flat £5 per month I think I'd be happy just to let it run indefinitely without worrying to much about it. At £10 per month I'm much less likely to do that.
Finally, with all those in place:
5. Get a really exciting campaign running and advertise the **** out of it on social media. Incentivise resubscribers in that period. (say if you resub during the even you get a free soul stone - something that is really attractive to returning players).
6. After the campaign event ends, have a weekly repeating event on one of the weeknights that lasts 6 hours or so. Make it really challenging but with high rewards so it attracts people to come back each week.