I'm about to start building a Nether tunnel and just thought to myself that, now since Mojang added waterlogged blocks to the game a while back, lavalogged blocks might be feasible as well, as long as it's no flammable material - even if it's just for decorational purposes. Small trickles of lava inside a stairblock or pouring outside of various openings. But I'm not sure if that would require an overhaul of the lava mechanics in general.
Another point would be to make warped planks and the related items flammable, at least if you intend to use it as a fuel source in a furnace. A few days back I crafted a surplus of warped stairs and slabs and wanted to get rid of the spare materials in a furnace, but couldn't. I can however put them in a trash chest, but I'd like them to be used as fuel as well, since the wiki indicates that they are "wood variants".
Last but not least, I want shears to be smeltable. Simple but the only right choice in my opinion.
Edit: Sry, another thing that came to mind is ice blocks and carpet. It's a little weird that you still get the speed effect of blue ice through slabs, if you ride a boat or walk over it, but I tried to ride a boat on carpet, placed on ice and it doesn't work. I'd like that to be changed.
Lava wouldn't hurt for a mechanical overhaul, but even if it doesn't get it, I think Lavalogging would be okay
That said, I don't think Nether Planks & related materials need to be flammable. They're Nether materials. It makes sense that they're resistant to heat, such that the only thing that can really "burn" them is lava (which, personally, I'd be in more favor of most or all Nether-exclusive materials having Netherite's lava resistance than for Nether Planks to burn in a furnace, but also that's kind of a unique mechanic reserved for super-end-game gear)
Shears being smeltable into an Iron Nugget would be okay