What we do know is that you will have until 30th September to use your points, this includes booking any free tickets that you have earned. Therefore if there's no immediate need to use your points you don't need to panic buy and use them on something you don't really want just so you're getting some use of them.
However, if you already know what you want your points on and (if it's free travel) you're within the booking period then it's worth booking now as we don't know if availability with Virgin Trains East Coast will be as generous. The Rewards Ticket Availability Tool lets you know whether there's rewards seats available on your chosen service.
Best advice is to book rewards ticket for your chosen dates as soon as they become available, if you need extra points to reach a reward have a look at "Topping up your East Coast Rewards balance". This method is the best way to ensure that you have the points for the reward you want, remember you won't earn any points for purchases from 1st March onwards.
Don't leave booking rewards until the last minute. When the September 30th spending deadline approaches there'll be increased demand when more people are trying to use their points and availability may be limited.
Will availability dry up in the new franchise?
It's possible that Virgin Trains East Cost will not release as many seats to reward card holders although history has shown that the new operator will continue to release the same number of tickets. When National Express took over from GNER they honoured the free rewards vouchers issued by the GNERtime scheme and the availability was the same, when East Coast took over from National Express they also kept rewards availability for members of their 'escape' scheme. Any shortages of availability is more likely to do with the increased demand rather than reduction of supply, this is why I suggest you should keep an eye on availability and book when the seats become available.