Restore choice between absolute (mm) and space-relative offsets in text styles?

In ver. 2.x text styles, it was possible to select whether the offsets were in mm or in sp(aces). This choice disappeared in ver. 3 (incidentally, why?) and now the measurement unit for offsets in text styles is unconditionally tied to font size: sp if the font size is sp-relative or mm if the font size is fixed.

I agree that this is the most common case, but when you need the opposite, you really need it. The major use case are lyrics. Text fonts have their best readability within a rather narrow size range, approx. 10 -12 pt for fonts with large x-height (like for instance Arial) or 11 - 13 pt for fonts with a small x-height (like for instance most Garamond's). Above or below this range, the readability degrades and, while reading one (or a few) words of a title or a tempo indication might be fine, reading a continuous text flow like lyrics may become more difficult.

It is clear that lyrics offsets have to be sp-relative (otherwise it would be complex to position them at the wanted position with respect to the stave); currently this requires the font size to be also sp-relative.

Assuming the practical sp range goes from 1.2 mm to 1.8 mm (smaller or larger values may perhaps exist, but are for special applications, for which special rules might apply), this gives that a lyrics text style size suitable for the minimum score size (say 11 pt) would become 16 pt at the maximum score size or, vice versa, if fine for the max., it would become 7.3 pt at the minimum.

There are workarounds, of course: making the calculation manually and adjusting the font size score by score, but this requires more work and repeated usability tests (in print, on screen, etc...) or multiplying the templates ("4 voices 1.2mm", "4 voices 1.4mm", "4 voices 1.6mm", "4 voices 1.8mm", "3 voices 1.2mm", ...).

So, the solution I found was to use an absolute font size (toward the minimum of the "best range" for the specific font), regardless of the space size and have offsets in sp-relative units. This is no longer possible in ver. 3.