I did note that potential problem.
That's why they'd get a form of trial VIP, like the old trial accounts. It wouldn't actually be VIP, so they wouldn't get premium and it wouldn't give them full VIP access, just a limited taster.
Back when we had trials instead of freemium, it was the equivalent to giving someone full VIP access until lvl13, so it was limited, but a taster. People could constantly make throw away accounts back then too, but they were still limited from the full content. This would be no different apart from requiring the extra steps of lvling to 50.
Not all players are scum who would do that anyway. Back when we had trials, we had something to try out before paying. Now they get all this free stuff and the constant question appears "Is it worth it?". All they have to base their judgement on is other peoples judgements and what they hear about, not from their own experience.
It could even be as little as a few hours to try things out and not even a week like the trial was, or some sort of token system that lets them try a limited amount of iTrials. I really don't see how something this small could defeat the whole purpose of upgrading, it could motivate some people to want to carry on as real VIP.
PS, what does RMT mean?