One way forward might be to use the “legacy mode” version that I did, which still allows the old escape sequences (that Swift for good reason did away with, as well as the $ for interpolation), in v0.7,
and maybe clean out uses of the legacy sequences $identifier in Base and stdlib as well.
Making FemtoCleaner work to change upgrade all of the uses automatically could be done later, possibly along with a compiler flag that causes usages of the legacy escapes and interpolation to give a deprecation warning.
I still think that 1) eliminating issues with having to quote $ all over the place for things like LaTeX sequences, 2) also not having to remember to quote $ when dealing with applications displaying monetary values (not just US, many other countries use the $ sign) 3) inconsistency with every other language that uses C like string escapes 4) avoiding coupling of the parsing with the Unicode character tables (to figure out when an identifier is finished) definitely trump a minor inconsistency between interpolation in objects (which isn’t nearly as frequent as the use of string interpolation, from what I’ve seen).