You won't get a source for it because there is none that they can provide. I didn't read their last post because I have them blocked now, but other times they answered this it was little more than napkin math based on their personal experience on only one server along with conveniently overlooking anything that contested their claim.
The only ones who know how many grandfathered plots are demolished every week are SE. I seriously doubt MaybeOliverB works for SE.
I don't know if you know this, but SE have quietly lifted the purchase restrictions on fc houses, so now the current limit is one private home and eight fc houses. A few posts ago MaybeOliverB informed me of this. SE's information about this on the lodestone is out of date. I suppose they quietly lifted it because they didn't want to encourage players to start hoarding again.
So I don't know if you mean the purchase restriction should be reduced back to what it was at 4.2, or if you were unaware that it was lifted.
The data centre splits makes me both hopeful and concerned. It does mean that many players who leave crowded servers will finally have a chance to get a house elsewhere, but this doesn't mean each will be a success story. I expect to see posts from people saying things like "I thought I would have the chance to get a house on <server> but all the wards are full and I can't transfer for a few days while the empty plots elsewhere are being bought. I'll never get a house." and "I left my house behind to go to the same data centre as my friends and the server I moved to has no plots left". We already saw similar happen before with the first free transfers. It's one of the primary reasons why those two players on Mateus became so controversial.
The only way SE could mitigate this without changing the system is if they bring in more wards at the same time, but as far as I recall they did not mention the intention to do so before 5.0. Of course they can at 5.0 but that's several months after 4.5.