I guess that's why they haven't releases the SDK yet - they just don't have all the sources anymore. I saw such a situation once, I was the one who had to develop new software after the previous main developer ... (to be polite) retired and left only binary compiled version to us.
it is of course hard to get internal informations, but in principle every company worldwide is doing exact the same -
1.you buy a company,
2.you plan merger,
3.you fire people because you don't need additional staff,
4.you will get blamed by customers/your product is not "working"
5.you hire contractors because you don't know what to do,
6.you hire again old teams to fix issues.
The good news is - Hantek is already between stage 5 and 6 (they did tried to fix some firmware issues and produced new once,
they released interim non-public fw versions (especially for new hardware) with big bugs, so finally they dropped pants and told the truth
to distributors about development issues due insuficient staff. That's fair enough and good starting point).
From what i know they have definitely SoC sources and at least CPLD/FPGA binaries and documentaton. Which is in principle enough to compile new
firmware (SoC) versions and to publish SDK, but not sufficient to change hardware revisions. The plan was to publish SDK end of jaunuary,
however due the internal dev. team issues they worked on bug fixing and new hardware revision (which caused new bugs).
Finally they deleted all firmwares from web page, dropped pants, and focused on the "right way to work". This is again a good example
for chinese companies, they working much faster than wester-world companies. I'm working since years with Fortune 100 companies on big projects,
and to be very honest within 6 months you will not get even trough all meetings, still light years far away from real work.
Hantek managed to buy, merge, produce mistakes, drop pants, hire people within 8 months which is
incredible fast!,
this is in my opinion another one reason to trust their products.
This means for us, we have to wait - for official SDK from Hantek/Tekway or for custom partial-SDK which is almost ready.
A user from this forum spend tons of hours decompiling the firmware and documenting things, let's hope he will publish it soon.