In this thread Nano states that "... no more custom themes for acp in v10."
This is not unexpected, nor am I going to raise objections as I did when it was 9.2.3. If a change of this type is to occur then clearly a main number version change (9 -> 10) is the best time.
If my module needs to adapt to use DF10 then so be it. But it has the potential to be a HUGE change, so I'd appreciate an early understanding of how this will work, so that I can prepare ...
In interests of common understanding, let's look at News. There are 2 ways to submit a story: through Submit News (user side) and Admin > Add Story (admin side). Different privileges available, different code = solid security. Both admin and user sides offer/require Preview, and this works for News as currently implemented (ie text only).
Asking user to create his theme modifications twice, once in his custom theme and once in acp is onerous work to place on the user, but worse requires custom alterations to the default theme.