consider the possibility of tilted Jres spectra (Hz/ppm)

I propose that you make it possible to display:
1) tilted J-res spectra. These spectra will have a chemical shift scale in the horizontal direction and a scale in Hz in F1. (typically 50 Hz in F1). Compared to a 1D spectrum, the multiplets would be tilted vertically (F1 projection: pure shift spectrum). I can provide examples. These spectra would be obtained by tilting J-res spectra or re-organizing DIAG spectra.
2) multiple quantum spectra. Usually Hz in F1. This would allow to work with 2D inadequate spectra. In general, the multiple quantum have scales in F1 are Hz, and vary with double the scale in F2.
Conclusion, generally, it would be nice to have ppm or Hz in both dimensions as default unit for 2D spectra. It means that the Larmor frequencies should be specified in F1 and F2 to interconvert.
In these two cases, what the projection would be may be different than for simple COSY; HSQC; HMBC.