The way you explain it, sounds pretty reasonable.
If only I could manage to get a little more free time before Christmas I may give this concept a go.
Suggestion: Why dont you start with BetterWB as a basis and then remove/replace components that are not 2.1 compatible? It shouldnt be that hard, and I can help you if you run into trouble.
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Gulliver, I finally got some free time to look at the enhancements included in BetterWB and filter those that are compatible with OS2.1. It turns out that the majority of the programs that you assembled into BWB are also 2.1 compatible. In fact, it is much simpler to instead list those that require OS3.x. Naturally, the improved Data types are useless in OS2.1. So, here's the list of 3.1 specific stuff:
Finder 2.06
Fullpalette (IMHO, the Palette.prefs from OS2.1 is superior to the one supplied with OS3.1. I'm not sure a palette locker is needed.)
IconAppearer
ILBM data type
JFifDT data type
PCX data type
PNG data type
Speak-handler (Apparently, this is NOT the last Speak-handler that Commodore included with OS2.04)
Targa data type
TextDT data type
TIFF data type
UnixDirs3
Visage39.22 (I will miss this one!)
WaveDT data type
A surprisingly short list, especially if the data types are excluded. Those above were the enhancements that clearly stated in their docs that OS3.x IS required.
The following is a list whose docs did not specify any OS requirement.
Avail (command replacement)
Boards
CX
Fat95
Mathtrans (originally Quicktrans on Aminet)
Monitor drivers
Next (text reader, I like this one. TextView is also very good!)
PSort
Serial (ArtSer) (There are other (faster?) serial replacements, like New8N1 on Aminet)
SmartWin
SwazInfo
XPKmaster
Another short list that needs to be checked for 2.1 compatibility.
Since 2.1 did not include Multiview, there are a number 3rd party substitutions that simulate its functionality. I have yet to evaluate those. The one written in E looks interesting.