In a thread at UO Forums about Ultima Forever, the UO Forums owner mentions that Ultima Forever could benefit Ultima Online.
Jeff Skalski, the Ultima Franchise Producer, over both games, responded with this:
I couldn’t have said that better myself. In my mind there’s no reason Ultima can’t be as big as Battlefield. There’s so much to do that’s been long overdue, but right now it continues with UO and starts with Ultima Forever. U4E is very different from UO even though it’s an online RPG. For those who’ve played the older titles in the series you’ll understand except now your companions will be your friends. We’ll take all the support you can give us, so sign up for the beta at ultimaforever.com and give us a shot. Britannia needs you.
There are big things planned for UO’s 15th Anniversary, which is just 2 months away, so it will be interesting to see how all of this plays out.