Yeah, the thing to watch now is the BBC opportunities page where their public tenders are announced. Until production of future Doctor Who seasons show up there, interested parties can't even pitch or submit a preliminary budget. And only then do we have a ballpark idea of the timeframe — assuming it goes like a recent tender for the hospital drama Casualty.
I believe it's a projection from the latter that has given the guesstimate that Who could be back on screen in 2028 at the earliest? I'm not sure that production will be quite as fast considering the amount of visual effects required for Doctor Who, but I'm optimistic 🙂