The UI gets a little slower at 50+ flow steps, so editing may be slow, but functionally it will work.
Just one important caution: Choices do not know which data value triggered the Smart Campaign. So if you're planning to have a generic "Data Value Changed" trigger in the Smart List, then using a Choice to find out which data value changed, that's not going to work. This is because a Choice is a "filter", meaning it looks back in the entire history of your Marketo instance, so if the field ever changed, that Choice will be selected.