There was an attempt in the early 3.0.x days to do prefilling of pools,
but the code was very broken so it was removed.
Maybe you would like to have another go and post a patch?
I might take a look at it - or maybe I'm just really naive... I mean, how hard can it be to preseed a pool, right? ;-)
Not hard. The problem comes when you have to refill due to discarded instances
and also take into account whether instances are not going to be returned to pool
because they have moved into cache.