The best way to match with common usage would be for 'This' to refer to days in the current week, and 'Next' to refer to days in the next week. This would require MLO to also take note of which day a user starts their week on (Sunday or Monday), or better yet, to separately ask the user when they want their 'parsing week' to start (eg my work week start on Monday, but my cultural week starts on Sunday - and this is likely to vary per religion/culture/language).
Alas, I suspect there where still be exceptions where someone would complain. Thus, maybe it still is best to use 'next' for the next day in the sequence, and to document that in the Help text. Then it works one (most logical) way for everyone.
In closing, I finally looked in the HELP file for how MLO implements this, and they have chosen their own logical approach, which is consistent, if also not fully adapted to actual usage:
Friday (nearest Friday in future)
next Friday (next Friday after nearest Friday in future)
This I can live with, and I am sure its easier to program around ;-)
-Grant