Decimal roman numerals is something I’ve never read about before, but I think it needs to be consistent with the numerals as we already know them.
The current numerals go IVXLCDM. That’s the increase from 1 up. But what about 1 down? I say we go with vxlcdm… except that one fiftieth “l” looks just like one “I”. So instead we can just go with k because it’s next to l on the keyboard and isn’t already used. But then sometimes roman numerals are in small letters not capitals…
w = 0.5
z = 0.1
k = 0.05
h = 0.001
e = 0.005
n = 0.0001
Rogue One is already just before Episode IV so that can be Episode zIV.
Solo will be set before that, but we need to leave room for movies just after Episode III, so half way is a good fit. It’ll be Episode wIV or, if you’d like, Episode IIIw.
If a movie comes out set between Solo and Rogue One, it’ll have to be Episode zzIV or Episode wzzIV.