I'll believe this when it's formally announced, not before. BT secured "exclusive rights" to the Premiership in December last year (The Beeb report
HERE is where I found the "exclusive" part). They will no doubt sub-sell a handful of games to CH5 as they've done in previous years as a way to try to spread the costs & as a hook to try to lure more paying viewers.
Last year/season was an anomaly in terms of showing all the games. BT were no doubt happy to have something to show & clubs could keep supporters on side by offering free passes to the streams to STHs. This doesn't make financial sense now fans are allowed back in grounds either for BT or for clubs. PRL would have to alter their contract with BT to now allow streams of games not being covered, alongside the extra financial cost of full broadcast crews if they were to cover the games properly. That's not cheap and PRL/the clubs are still counting the cost of not having matchday revenues from last season.
That's not to say that when the rights are next up for negotiation we won't potentially see someone like Amazon take an interest. They already have the AIs following last seasons Autumn Nations Cup & seem eager. That would allow CVC to sell a global package worth a lot more than just the UK/Ireland package at the moment so would be a target for them. I fully expect that the rights then could easily move to an online platform, particularly if CVC can package them with AI rights, the Pro16 (can't remember the new name for that!) etc.