Thanks for asking.
First of all (as a former Finale user) I would like to say that I love the look and feel of Dorico and I think the program (although quite advance already) has a lot of potential. That’s also why I’m so serious about this.
To answer your question: “It depends”
For a theoretical analysis (or when teaching someone harmonic functionality) I would want the possibility to use either symbol because it all depends on the voice leading and the function of the chord. (See excerpt in jpg).
For my own writing I would probably favour b10 from a functional and voice leading standpoint because that is the way a minor third in a dominant 7 chord is used in the majority of the cases.
To be fair though, for practical reasons I would choose one consistent way of spelling throughout a piece for convenience and readability and I would favour b10 above #9 for the above mentioned reasons.
Of course I know that due to the American educational system the use of #9 is dominant and I have no intention to fight it, I’m not the Don Quichot of chord symbols. And I can see why the they abandoned the b10 to simplify the way you can teach students chord structures, although thereby alas sacrificing to correct describe the functional behaviour of most dominant 7 chords with a minor third added.
On first glance it may seem like a futility, and to those how never seen the use of a b10 (and the theoretical meaning of it) it may look strange, but since Dorico also supports extensive possibilities for microtonal writing and playback (which to me is more of a niche thing then the proper spelling of a Blues chord) I think it wouldn’t be too much to ask for an easy input (via shift Q) of a b10 chord with or without a combination of other extensions.
I see that b9 #11 ect. are one typeface so taking the b13 typeface as a starting point for developing the b10 typeface would look like an easy way to go.
Hope you will consider this possibility and implement the b10 possibility within the overlay input.