As a huge fan of DK Remix, I would prefer consistency between the DK Remix and DK Jr. Remix. I like the Jump button switching. It works fine for DK/Remix/Deranged. Just one fan's opinion. I like how you have Luigi making an appearance.
Using the jump button (from attract mode) to switch between DK Jr. Remix and regular DK Jr. will still work the same way as it did on the DK Remix kit. The new thing I've mulled over is that DK Jr Remix will *also* allow you to play the original DK Jr. stages/level order without needing to switch back to DK Jr.
The difference in this case will be that this version of "Classic DK Jr." will be running on the DK Jr Remix engine. It's going to include the improved control response, glitch and bug fixes, 1 million points digit, 2 digit level display, etc... that is part of DK Jr Remix. Classic will also have it's own high score table.
It'll still let you switch to the original DK Jr ROMs and play the original, unmodified DK Jr. But there will be a new version of DK Jr as part of DK Jr Remix as well. All 3 will save their own high score lists too.
It's not all actually implemented yet, I'm still working on that but that's the plan right now.