solo should be a radio-button
First, you should do a tutorial video on the way the solo and mute buttons should be used as intended, because perhaps it's just just me that have the wrong assumptions.
The manual says: "Solo this track Only the sound from this track can be heard." That's not really what happens.
The way I expect the solo buttons to work is the same way as radio-buttons do: only one can be selected at a time, selecting one unselects the previously selected button.
I saw the option-click that was added, but it does not help for the solo buttons. What it does is a apply what you're doing to a single button (either press or unpress) to all buttons, so for example if you had a track solo'ed and you wanted to solo (only) another track, you'd have to click on the track you want to solo (to turn it on), option-click on it again (to turn all other tracks solo off) and then click again to turn it on. That's not faster than going to the currently solo'ed track and turning it off, then moving to the track you want to solo and turning it on. Nothing gained.
That's a great feature for the mute button (option-click), but not the behaviour I'd expect for solo. For the solo, if the normal click stays the same, at least the option-click should select solo on the track and removing solo from all other tracks.