For what it’s worth, I’ve been accomplishing a specific ordering of my subscriptions. What I did was sort them by name, prefixing all names with a two-digit number.
Please feel free to either use that as a suggested work-around for the lacking functionality, or as an indicator that at least one other person has desired manual sorting.
My need of manual sorting practically went away with the introduction of tags on subscriptions in version 2.3.0, but I guess there are other use cases still.