1-10 scale difficulties

This really isn't about Stepmania, but how do you think some new boss songs (and some of the old ones) should have been rated on 1-10 scale? The scale can go higher than ten if it has to.

Example (without difficulty bias):

Valkyrie Dimension
Beginner: 7 (around as hard as Trip Machine, maybe a little easier)
Basic: 8 (It was a 12, not a 13, to be honest.)
Difficult: 9 (That is not a 10. I'm sorry.)
Expert: 13 (A low 13, but a 13 none the less.)
Challenge: 14 or 15 (Second hardest chart ever. Paranoia Revolution Double Challenge is harder, though.)

The scale can go higher than ten if it has to.

then... why are we limiting ourselves to 1-10?

Old scale = scale used in DDR games pre X (1 - 10) and In The Groove scale (1 - 13)

DDR X scale is pretty much old_scale*1.25. To get old scale ratings you just need to divde by 1.25. Sometime they are rounded up, sometime down. Some songs are much harder than everything that was in ITG thus it's natural that they would be 14, 15 or even 16 (for DDR X 19-20 rating).

Old scale = scale used in DDR games pre X (1 - 10) and In The Groove scale (1 - 13)

DDR X scale is pretty much old_scale*1.25. To get old scale ratings you just need to divde by 1.25. Sometime they are rounded up, sometime down. Some songs are much harder than everything that was in ITG thus it's natural that they would be 14, 15 or even 16 (for DDR X 19-20 rating).

I always used 1.5 as the multiplier. Hard DDR charts aren't even kind of comparable to hard ITG charts, an ITG 16 *should* go off the end of the DDR scale...
I wrote a (Python) script for it a while back, I've been satisfied with the results: https://gist.github.com/shakesoda/7713536 (note: only deals with .SM, which should account for the vast majority of 1-10 rated files. also, it works in reverse if you switch multiply to divide on line 59)

I used to use 1.5 as a multiplier, based on the old '10s' being rated 15/16, but the hardest couple DDR songs( the 19s ) are 14s on the ITG scale so maybe +5 is more accurate for the higher end of them. It's hard to compare the old/ITG scale where the difficulty tended to be more physical to DDR charts where most of the difficulty is memorization based( crap like VD ). The "1-10" scale has been fleshed out pretty well up into the 21+ range with ITG customs.