Board Thread:The Panopticon/@comment-43908-20150311013943/@comment-4028641-20151105021506

Here's what Czech says:

Importantly, the occasion of this quote is the run-up to Romana's Reaffirmation Ceremony, where she reconfirms her oath of office. The implication is pretty obvious — Romana II came to power after Warriors' Gate and has been in power so long and so continuously that she's regenerated, become the Cornell version of III, and now has to reaffirm her oath of office. This is the successor of Romana II.

Indeed, this isn't just speculation. The Doctor explicitly says the Reaffirmation Ceremony is necessary because she's been in office for 150 years.

Now he's suggesting that the need for the ceremony is that she's regenerated, yet he also claims that 8 suggests that it has to do with how long she's been in office period. In fact, despite him claiming that this is definitive proof and far from speculation, I'd say that there's still no in-universe evidence of it.