If you were going to do that (seed them near the homeworlds), I'd vote for seeding two, one next to each. However... I'd like some clarity as to what you mean by Core and normal Fabricators.
The 6.013 patch notes refer to Snipers, Shredders as Core Fabs, but if I recall correctly the game doesn't. The galaxy map filter lists three kinds of fabs, but the wiki currently refers to only two types; experimental and core.
If you're proposing things like vampire claws get stuck next to AI Homeworlds, I'd be against that.
I presume you're proposing this change with regards to Starship Fabs get moved there. I'm neither for nor against that, haven't grabbed MKV starships yet, but I might have one lined up in my "AIP Stress Test" game. If we were going to do this, I'd wonder where the "Beam Starship" and "Warbird Starship" fit in the scheme of things. Is the "Beam Starship" even relevant, if not redundant?
Without considering all the balance concerns, I'd be quite amused to have the entire set of MKV starship fabs located on each homeworld. Incentive enough not to take them out simultaneously? Well, rationally, no. In terms of toys to play with, it'd be quite tempting.