I am sorry, but the development of TemplaVoilà 8.7 will not be continued.
tl;dr There are too many issues with the flexform handling of the core.
I started making the codebase TYPO3 8.7 compatible, which was quite easy so far. However, there are still bugs in the core regarding the handling of flexforms, thus I do wait for some patches to be applied to the final version of TYPO3 8.
I decided to not continue the development of TemplaVoilà for TYPO3 8.7. The main issue is basically the new implementation of the form engine that has a much stricter flexform handling than before.
Making the extension itself compatible with 8.7 isn't actually much of a problem. It all boils down to the very error prone data structures (flexforms) that are already hard to handle in 7.6. There would be even more manpower needed than for the 7.6 to make TemplaVoilà more or less independent from the core to not always just spend all the time and money in adjustments but new features.
Unfortunately I do not see enough demand of these still using TemplaVoilà. Also I couldn't manage to find a team of developers that are interested in joining the maintenance. Quite a lot of the former sponsors told me, they would use TemplaVoilà with 7.6 but would eventually migrate to a core solution afterwards.
As sad as is it, I am not the one who can keep that project alive. Mostly due to unpredictable changes in the TYPO3 core itself.