3 year old Tivo premiere xl4 - lifetime?

Hi
So I've had my Tivo 3 years and now considering going for lifetime subscription instead of the monthly subscription.

Welcome any advice on what I should expect to pay or whether I should switch to a new Roamio/bolt with lifetime?

I assume I can sell my xl4 but know it's worth more with lifetime subscription included

Lastly, I've heard rumors of a new Roamio or bolt pro coming out - any ETA on timing as happy to wait if not too long.

Thanks in advance
Rob