I don't think Playtonic could afford them right now. But that's not a bad idea. Maybe once Playtonic have a bunch of games behind them and have amassed a fortune they'll be able to afford the IPs. But by then they won't need them anymore...
Yooka and Laylee is a much more interesting pairing than Banjo and Kazooie ever was anyway, so if they intend to continue making games with them, I don't really see the need for them buying the Banjo-Kazooie IP.
But Conker's a much more unique character, and Rare/MS don't seem to be doing anything with the IP, so that one might still be worth it for Playtonic to pick up in the future.