If you have "day of year" as a dimension you can leverage that with YTD (or whatever period you need) segmentation applied.  You'll have to also build a fiscal calendar table to link "day of year" with an actual date. This worked on my end but it was very time consuming and doesn't feel like the mos...

this should absolutely be fixed and should be part of the MVP, the 2.0 API is useless without it and shouldn't even be released in a beta without it

Can you use a cohort table?