The "jscwlib" Morse generator (currently the default here on LCWO) can handle non-integer speeds but there are a million places on the site where speeds are handled as integers in the database. I am afraid that will be quite an effort to change this, although I like the idea to allow a better granularity.
One idea would be an user defined setting to switch between WPM (words per minute) and CPM (characters per minute) throughout the whole site. With CPM you basically get 0.2 WPM resolution.
I added it as an issue to the tracker and I'll think about the implications... https://git.fkurz.net/dj1yfk/lcwo/issues/20