I think it is important to make it just different enough that people do not confuse it. 19.10 btc is very different from 19.01 ^btc.
How about something like 21100 ^btc = 1.00 btc, so 205 is a cheap pizza, 1994 is a USD, etc?
OK, I'm liking that. It alludes to exponentiation whilst being different enough (both from 'mathematically correct' exponentiation and from a simple decimal) to be immediately recognisable. As the 'native' way of writing power bitcoin I think this could work.
There's a disadvantage in that it's not as simple to do with a keyboard as just typing a character but my first impression is the advantages outweigh that. We'd also need a way of verbalising it and of communicating ^btc numbers in plain text for instance for use in SMS where
sup is not an option. And maybe this same plain text representation would be usable in a spreadsheet in such a way that that a formula can separate out the elements to do calculations then express the result back in the plain text representation. Ideas anyone?
In bitcoin wallets and on web pages with ^btc functionality there could be two textboxes with relative font sizes and positioning to reflect this visually so in order to type in
211 one would just type in '211' with the cursor simply moving to the significand textbox after the first two typed digits. Where a single digit exponent was required '01' could be used or just '1' then Tab to the next box. I can see this working.