First of all, if something like this was already said / proposed, I have not come across it. I read forums from time to time, but not everything.
Let me start by stating the problem I see:
- Wild is discouraging new (regardless of f2p or buyers) players to enter it, and existing f2p players without full collections to keep farming old cards. Reasons being no competitive support, limited / secondary balance support (depending on how much you buy into Blizzard statements after already having the experience of reality), and mostly removing old sets from shop.
- Standard is about spending $ quickly enough (how much is enough and how quickly is quick enough is debatable, but it is about spending nonetheless). This is again discouraging for new, existing f2p, and especially new f2p players to enter.
If you are interested in my explanations behind these statements, you can find my posts in forums posted after the formats announcement.
What I think could help a lot with these problems is very simple - make the old sets obtainable similar to core set - something like achievement rewards. Whether the system will be fixed - as it is currently - you get exact predefined card at some class level, games won etc., or it adds some sort of customization - achievement points, and rewards are priced for these points (lot of games have this, maybe even WoW, I don't know), there are options for sure.
How it helps:
For Wild (which Blizzard is already treating like secondary / not fully supported) - you remove the ridiculous entry barrier for anyone not having those cards - new, and f2p. Also makes everyone wanting to still collect old sets happy. It doesn't mess with Standard and competitive "freshness" / balance.
Counterargument (which I can think of) - less $ from Wild for Blizzard, since it will not be such a huge dust sink. However, I don't think Wild will be very profitable - the dust sink seems to be putting a lot of f2p playerbase off rather than motivating them to collect the cards for higher cost. Instead of killing it (which I exaggerate a bit, but not really that much), make it work for you with the parts of playerbase, where Standard ($ entry barrier) does not appeal as much.
Currently Blizzards treatment of Wild and the removal of old sets from shop just creates angry pushback, while not gaining anything (in my opinion). You already get $ from those willing to pay with Standard. Entering HS as new f2p player will be harder by magnitudes. Proposed change makes the exact opposite - existing f2p players without complete collection, and new players, can have Wild and collecting of old sets as friendly (no $ commitment necessary) way of entering and staying with Hearthstone for a long time. This way you keep / get many more existing / new f2p players with much friendlier proposal / approach. I believe the non-direct advantages of having more players should be quite known - they attract friends (possible buyers), they might spend themselves after time, you get bigger community, more interest, higher coverage in media ... And i also believe it will outweight any $ gains by current restrictions on Wild and old sets.
Unless the goal for Wild and old sets really is to let them die over time. But Blizzard is trying very hard to convince us it is not, so here's a way that will help more than promises towards keeping (targeted new and f2p) people happy.