Reading between the lines of the recent announcement it sounds like the team are prepping their original Elysium hardware for the PvE realm (which they suspect will continue to be lowest pop server of the initial 3 realms) and will then bring up and upgrade the old Nostalrius servers for the old db PvP realm and the fresh start realm after that. By establishing a certain level of expectation now they are giving themselves some breathing room to manage demand and distribute the population in a relatively healthy way to at least give each realm the best start.
However, I do feel that it's a mistake not to launch the old PvE realm at the same time as the old PvP realm. Given the currently planned rollout it would appear that the PvE realm will suffer most if it launches some weeks after the others.
My take on the 3-4 weeks comment is that it is pretty fluid and reflects the cautious approach of the Elysium lead devs/admins who may be daunted by the behemoth they are about to unleash and perhaps wonder whether they have the capacity at the moment to manage such a huge operation even with the return of a number of the original Nostalrius crew. I'm sure they have the collective ability do it, yet it is a massive undertaking from a private server project that peaked at 1-1.5k players (even with all the years of Valkyrie uptime experience) to a project that could easily explode to 10-20x the size over the next few months.
In terms of the old PvP vs fresh start argument both sides need to respect the other's perspective. There's way too much vitriol on both sides at the moment. The key thing is that the communities on each realm are given the best start to grow and prosper.
Exciting times ahead.