Give people a soapbox, and some will inevitably use it to loudly assert their own needs, wants, and entitlement.
A handful of success stories selectively sampled from a multitude of games which have implemented the F2P model is not a good argument for UO's compatibility with the F2P model because it disregards a broader context (F2P implementations in the games industry as a whole) in favour of a blinkered view (successful F2P games). F2P can be massively profitable, or at least has been for a selection of games. However, this is simply not the case for every game it's applied to.
Being able to play a game for free is great, but what changes would need to be made to make UO profitable while F2P? How will gameplay be impacted, what new rifts will be created among the player base, and what will happen to our in-game economy?
Vast, significant majority of current, active MMORPGs are F2P now. I bet they all made a drastic mistake of ...let's see here...
"disregarding a broader context (F2P implementations in the games industry as a whole) in favour of a blinkered view".' : p
Anybody who doubts potential and functionality of F2P should look into the story of Old Republic.
You are absolutely right, some F2P games prove huge hits, some do worse. This is the case with any and every other line of commercial product ever made I recon. It isn't saying much about anything.
UO as F2P would prolly be something like this:
* Very little change for existing subs. You keep playing the game, paying a monthly sub for it and have more or less the same experience you have now. With possible and significant exception of having a lot of new players around you.
* Lot of new players. Most of them start and stay as F2P. Housing is behind paywall. That alone would propably make a large enough carrot. Perhaps shut the ability to use/benefit from powerscrolls behind paywall too. Maybe have insurance for subscribers only as well.
* Item shop is usually key moneymaker for an F2P game. Old Republic for example makes around 50% of it's incom via cash shop. This is a typical F2P feature that has been part of UO for a decade or so already. Active players already use it a great deal. It only needs more goodies, better accessibility and independence from Origin.
List of F2P MMORPGs from top of my head. Most of these are available in Steam. None of these require monthly sub to play. Most of these cost nothing to acquire. I recon all of these have more visibility and players than UO.
The Secret World* (Published by EA)
The Old Republic (Published by EA)
Dungeons and Dragons Online *
Neverwinter
Lord of the Rings Online
Rift
Runes of Magic
Aeon
Age of Conan
Star Trek Online
Everquest
Everquest 2
Runescape
Guild Wars
Guild Wars 2
Lineage
Lineage 2
Two of five most played games on Steam today are F2P too. ( Team Fortress 2, DOTA. ) Both of them have proven to be huge money makers for their developers. Even Blizzard's latest game is an F2P. World of Tanks, League of Legens are success stories so colossal in scale that everyone interested of gaming as an increasingly dominant slice of popular culture must have heard of them already.
Five or six of the games I've mentioned made more than 100 million for their devs in 2013. This in F2P earnings alone. I wonder how many success stories (SWTOR), smash hits (World of Tanks) and pop cultural phenomenoms (DOTA) it takes til you figure it is prudent to stop dismissing mentions of F2P as some irritating background static that couldn't possibly work for UO.
F2P doesn't need to be a - gigantic - success to do some good for the game either; Turbine has been very vocal about how going F2P saved both of their MMOs (LOTRO, DDO) from an axe few years back. Neither of these games is huge. Both of them are very much alive, with more players than UO. In 6 years, DDO went from 2-steps-away-from grave to seeing it's first actual expansion thanks to F2P. I think LOTRO switched like 5 years back. It is still alive, still kicking and still seeing new expansions today.
What personally irks me is how people against F2P so often, so easily like to imply people wanting the switch are doubtless somehow shady;
"unwashed greedy peasants who want to play mah UO for free!!11 Good thing I'm wealthier, better looking IRL and can afford to pay for my game!!"
People picking approach similar to above forget they preach to the choir in this regard. Most all here have at least one running subscription: F2P would not change way *I* play or pay for the game nor would it change way *you* play or pay for the game. It would bring more people and more life for you and me both to enjoy. This is what makes it a huge deal. Nothing is more important to an old MMO than stream of new players. It makes the game more fun for you and me. This is why so many existing subscribers want F2P so badly.