Anyone that meets the similarities that all three possessed, yes.
Trademarking, not copyright, of a term already in use would probably be denied unless the USPTO failed to properly research it (which I doubt).
You run a role-play (enforced?) MUD. Your game does not meet the historical definition of the term, merely the bastardized use which has served to confuse the general MUD community. Using a term RPI beyond the original intent is similar to calling your game a PK MUD. The use of the term would be confusing. But use or non-use of the term RPI does not change the quality of role-play found in a MUD. That's dependant upon the staff and players, not the terminology used to describe the features and policy.
And I have tried out New Worlds (twice, the second time at your request if you recall) and did not find it similar to Armageddon, Harshlands, Forever's End, Shadows of Isildur, or any of the other games which all bear the same characteristics to which the term RPI was first applied.
I might add that at least one attempt has been made to take the Argila codebase (a cleaner version of the RPI Engine) and use it to create a non-RPI MUD. I'm not sure as to what code changes they have thus far made but policy-wise, they've got no RP-enforced policy and as it was described to me seemed to be a PK MUD (though my memory on the details is foggy because as soon as I was told the game wasn't going to be used for role-play, I sort of droned out). There are also lots of other level-less and skill-based MUDs out there but that too does not denote RPI (and in many cases they don't claim to either).
And that's great. More MUDs should do that. But the entirety of the role-play enforced community is not seeking out the features and characteristics of what became known as RPI MUDs. That was why coining a term to describe that particular code/policy format became a good idea. As not everyone was looking for the same thing in role-play enforced MUDs, a different term was needed for clarification. Over the years, the abuse of the term has nearly rendered it useless again just like role-play enforced failed to originally differentiate different code/policy styles enough.
I discussed the wording with Wade a lot and, unlike me, he's not as verbal about taking a proactive stance on such things. He was also more liberal with the use of the term (indicating that the term RPI probably didn't originate from use by Forever's End itself, merely in reference to it). In the year before he stepped down, he was preparing for the implementation of the term RPO however because the massive difference between what he had always thought of as RPI (the traditional usage) and what was being employed by so many MUDs (several games that had role-play ACCEPTED policies created listings on the site), it was clear there needed to be further clarification. This brought out complaints from some MUDs listed on the site, notably only those that didn't meet the original use of the term. Real-life issues (common theme lately...everyone, myself included, seems to have had a rough couple years) as well as I suspect some disgruntlement at the controversy delayed implementation of the RPI-RPO differentiation which was supposed to have gone into effect over a year ago. The former continues to slow down reorganization of the site under the new management as well.
My apologies if I seemed harsh. I do appreciate the use of "think" and "believe" to denote an opinion from a fact though. Thank you for the amended use.
And again, I will state that RPI does not imply greater or lesser quality of role-play. As a former staff member on my game once said, "You can RP in a cardboard box." And he's right. I only lay claim to the use of the term as it was originally applied. Later use was not in keeping with that and has only led to confusion and a weakening of the usefulness of the term. Perhaps there was a perceived notion that the role-play on the three RPIs was greater than that of the rest of the Role-Play Enforced MUDs (I would agree, though my personal thought is that the quality of RP on the two remaining RPIs is dramatically lower than it was when I first started playing them). But that need not be the case. The standard use of that term was for a small subset of similarly-coded games. That was the original use and for a time the only one.
Questioning it is not offensive. But it is contrary to the historical precedent and only adds to the confusion that has arisen since around the millennium.
Jason