I like the general idea of burning assets for other products.

However, personally I think we should let the Riftwatchers burn like they are. Tt's actually a really good thing to have rare cards that can become expensive.
The more examples of rare expensive cards that players see, the more willing they'll be to go ahead and buy some of the current cards/packs in hopes of similar value increases.

So I'd be all for a future set that is only available by burning previous cards, but will probably vote against this specific proposal because it involves saving Riftwatchers packs which were overproduced and are currently being burned down to a more reasonable circulation.