Well I am Torven so I can speak to this. The source will very likely open sometime this year and the fork has already been made and is being prepared. There is a small handful of things we don't want visible -- anti cheats and CSR messages -- that won't be made available, so we'll still have a private TAKP fork. Much of our project has already been leaked to some people anyway against our wishes because we've been generous with access to it and somebody took advantage of that, so if we broke our promise they would just make a public fork to spite us regardless. (minus recent commits) Although we never had any intention of breaking the 1-2 year promise anyway, so the threat is not the reason we will. I wouldn't have joined the team if it were closed source to begin with.
We were open source for about a year after we launched Classic era then closed because some disgruntled banned users took our project and created a server with it overnight and did everything they could to get our users to switch over to their server, which included a lot of plagiarism because they couldn't have openly stated that they relied on our work to operate. This was very demoralizing as you can imagine, so it was either close the source or shut down. For awhile in Kunark era we had like 30 accounts logged in during prime time every night on a 3 box server. Even if you don't have hostile servers trying to attack your project, splitting the userbase of a very small community of classic EQ enthusiasts is detrimental because you need a critical mass number of users in a game that requires grouping to advance, so it can be undesirable to have randos starting new servers all the time and splitting everybody up. Users do not vet the servers they start up on so it's false to assume that they will gravitate to the most well-ran server, and most of these servers will just end up dying in a year or two so they're not doing much good.
Another reason for the delay is because we don't want players digging through the code and database for spoilers. The argument that "everybody knows everything about the game already and spoilers for it all are already available" is not true and frankly a little insulting to me because if it were true I wouldn't have to do so much work. Years back we had users looking through our database and scripts for bugged drops and spawns then taking advantage of them instead of reporting them. Our Quarm is also very custom because our clients lack the final Quarm's spells, so I had to cobble together a frankenquarm using our spell data and some custom behavior, plus I took the opportunity to make him not a pussy so users could enjoy it more. We wanted guilds to figure him out before opening back up.
It's flattering to be called a potential p99 killer but I don't think that's true. Users don't really care about accuracy that much. P99 is simply accurate enough that other things matter far more, like their box rule and administration. P99 probably has better accuracy than us in some areas anyway. (our classic era zones could use work) People REALLY underestimate the value of p99's administration. Policing a one box server is a shitty job that nobody wants to do. P99 has that plus effective anti-cheats plus massive name recognition and mindshare that is very unlikely to be overcome. Also a non-trivial amount of work would be required to make a Velious era fork of TAKP's backend, so it's not just a client swap. (which also requires significant work)