Top things I want in Mario Maker 3:

This new update has made me a Mario Maker, uh maker instead of just a player. I've made 2 casual levels using  the new elements: Koopalings, Frog Suit, SMB2 shroom... I have been experimenting with Super Mario World, New SMB and I have seen the limitations of SMM2...

I KNOW Nintendo is paying attention to bloggers, YouTubers, and the ROMhacking community for Mario Maker stuff. Of course, this is a tiny tiny blog unlikely to be on the Big N's radar... but in the case they ARE checking me out for ideas, here's SOME ideas:

Fully Fledged SMB2 theme:
The SMB2 Mushroom should make a comeback for SMM3, BUT it would be interesting to have a fully fledged SMB2 theme. Since that game has a different Health mechanic than SMB1,SMB3, SMBW,NSMB, it should get it's own mode. Not to mention that making true SMB2 styled levels in SMB1 mode and losing the Mushroom would make the levels unplayable.

Multiple music themes:
For example SMB3 has 2 overworld themes, but on SMM2 there is only one.
Same thing happens with SMW.
For SMB1 they could borrow music from Super Mario Land 2.

More enemies:
Charging Chuck, Sniffits, Ninji, Shy Guys, Bombshell koopas, Nokobombettes, Rex, etc.
This one is self explanatory. Variety is the spice of life and th e more variety we have, the better.

More bosses/mini bosses:
Tatanga, Wario, Waluigi, Reznor, Piranha Pete, etc. There are plenty characters that can make the jump into 2D Mario adventures  and feel organic to the 2D platformer genre.

Sloped Semi Solid Platforms:
This one is an obvious addition that was missing from the Mario Maker 2 game. This would make for some interesting slides in combination with solid ramps. Not to mention that it could allow to create some Donkey Kong inspired Madness.

Alternative Exits:
Key Exit, ? Orb exit, giant P-switch, etc. Now that we have World Maker, these items have gained new value and importance.

Additional Power-ups:
Things like Ice flower,  carrot, hammer, metal cap, hammer bro suit, etc. These would add some variety in gameplay... especially if some of these are limited to specific modes.

WARIO AND WALUIGI:
The perfect unlockable once the player beats Story mode. They would not necessarily be the same as their boss counterparts to fit with the rest of the characters. They can even justify it within story mode.

Well, that's about it on the top of my head ideas.