Just do a 1/1,000,000 semantic stock split and be done with it.
Call them Bitcoins.
If I thought that could get broad consensus, and the switchover carried out without too much transition damage, I'd favor it. Obviously, the sooner, the better, because each day of writing/coding around existing units bitcoin/millibit/microbit makes the switch harder. Still, I could be convinced.
But, if as I fear it's too late for that, or too late to do it in one big switch, then 'zibcoin' offers many of the same benefits as a 1/1,000,000th 'bitcoin'. Same # of syllables, similar sound, compact unambiguous abbreviations (Z/Ƶ/ZBC). It can be used as a trial/placeholder.
And if your ultimate goal is rebasing the 'bitcoin':
I actually think if 'zibcoin' catches on, it might become
easier to someday revalue the headline Bitcoin. Zibcoin adoption means there are fewer labels/lines-of-code/stories that cement the classic, giant-bitcoin (BTC=10^8 satoshi, mBTC=10^5 satoshi, µBTC=10^2 satoshi) values into permanence. If day-to-day values are commonly quoted in zibcoin, casual adoption is smoothed, and the idea is planted that the "core Bitcoin system" is separate from its units, and can support multiple units.
And then, when "Bitcoin" is mainly used to refer to the system-as-a-whole, or the unit from the 'olden days' when you could get a million zibs for a dollar, then you could incrementally say... "OK, let's just call zibcoin units 'bitcoins' again." The zibcoin/zib words would be serving as the middle-step of a safer transitional process – a bit more like how soft-forks happen in stages, only taking full-force when most miners are ready. You then wouldn't need total consensus and synchronization for a giant 'flag day' incompatibility cutover.