The ONLY reason we got R/B/Y was the 20th anniversary. Even if it makes absolute for them to release them all, the others definitely aren't a sure thing.
The thing is though if TPC/GameFREAK redo G/S/C for Virtual Console, there's gonna be a price increase for the games.
For R/B/Y on VC, they changed Jynx's skin color, offered a number of regional ROMs, plan to add Bank compatbility, enabled access to the Surfing Pikachu mini-game in Yellow, and allowed the link-cable functions to use the 3DS's wireless Download Play feature which raised the prices to 10 bucks each. If TPC had just simply ported them instead, it would have been 3 bucks each. Game Boy Color games usually run about 6 bucks and if TPC treat G/S/C with R/B/Y care, I can see the prices going 12 or even 15 bucks each.
All of those changes except for wireless multiplayer are extremely small. They didn't reinvent the wheel, they swapped out the 2-color palette for a 36x36 8-bit sprite and permanently set a single variable used in a single if-statement to true. Uploading multiple region-specific ROMs is a literal non-factor. Furthermore, the wireless functionality is emulator-side, not the ROM, and that functionality can be applied to any gamelink-compatible games, G/S/C included. Bank functionality is just the bank being programmed to look for and alter the save data for R/B/Y as well, and again that's trivial to expand to G/S/C. It's also handled by a different team entirely, and is more the Bank and Sun/Moon teams capitalizing on R/B/Y being available rather than a true added cost. And G/S/C will likely require less minor tweaks.
So the only real, significant cost-adder is the emulator, which is already a sunk cost.
Plus, R/B/Y were never, ever going to be $3. They were always going to be "premium" downloads.