I have added Sonic 1 zone compatibility to the ProSonic engine. Sonic 1 levels use 256x256 tiles, and most of the other games use 128x128. The 128x128 format has been native to ProSonic since the beginning, but with Sonic 1 compatibility, you can load levels using the 256x256 tile format too, so no conversions are required. In addition, the engine also supports 32x32 and 64x64 tile formats. Your game doesn't have to be limited to just one of those formats either, you can use them interchangeably. So you could have two zones for example, one using 64x64 tiles, and the other using 256x256 tiles. I figure this works nicely for team projects where different designers have different preferences. Hopefully people will find this flexibility handy.
Shown here is a screen shot of ProSonic running Green Hill Zone from the original Sonic the Hedgehog game. The downside is that because RAM in that game doesn't store the ring layout, there is no layout for rings in the level when being played. Of course people could either add objects to it, or they could import from the ROM. My LIMP utility doesn't support gathering data from the ROM, but this should certainly be a goal to work towards.