Dear @rinigus,

thank you for your reply.
Let me address some points:

Well they shall not be afraid of this "aspect", but probably they are by "considering it".

This idea (license proliferation across well defined APIs, in contrast to using a library you technically link to / a "link time dependency") is repeatedly propagated by the FSF (even before the GPLv3, with the GPLv2) to fulfill their (day)dream (or IMO: nightmare) of most Free Software (FLOSS) automatically becoming GPLed software sooner or later (and some proprietary software, too) by "this legal mechanism".
Unfortunately stating this loudly multiple times (and over decades) made many even more afraid of the GPLv3, the *GPL* family of licenses and the FSF, especially in commercial environments. I can comprehend that well.

TL; DR: There is no license proliferation across well defined APIs.
Think of Database Applications becoming automatically licensed as the DBMS they use (e.g., Oracle) due to the SQL API, but at the same time licensed as the OS they use due to syscalls, and concurrently licensed as .... this is nonsense leading nowhere and no reasonable court will follow this.

Yes, this is also my impression.
Thank you again for pursuing this.

Yes, unfortunately this sounds probable.

As stated, I started writing a personal letter, then decided to make it an public one, reformulated it a bit for this purpose plus added "P.S." & "P.P.S.", and posted it; basically to make the thoughts I repeatedly had WRT the "ancient Qt issue" more widely known.
I initially did not think about "confronting" Jolla at their forum with this open letter, but this would definitely address my goal "increasing pressure for Jolla to make a decision ..." better. So while I know that some sailors are reading at TMO, they usually do not post here, so posting at FSO makes sense, even though I still do not really expect a (substantial) reply there, either.

But I feel that will need to be done properly to have a slim chance of achieving something:

• Enhance some sentences (i.e., their "wording") to sound nicer (towards Jolla).
• Maybe it is better to address Jolla directly, instead of you. I still would mention your recent inquiries WRT the "ancient Qt issue" as the trigger for the letter, so you are directly invited (per @mention) to comment.
• Search for and link to sources of Jolla's former public statements WRT the "ancient Qt issue" at TJC, FSO and the "SFOS community IRC meeting" logs.
• What shall I conclude with?

  1. A plea to finally do any practical step towards a newer Qt (technical and practical)
  2. A plea to finally make a decision and communicate a plan WRT upgraded Qt releases for SFOS (organisational)
  3. A plea to seriously reconsider the "GPLv3 ban" for SFOS (license strategy)
     While this might have resolved Jolla's non-technical issues with newer Qt releases a while ago, the current conditions for commercial licensees (i.e., who is defined as such) may counter that. Another point to research.
  4. A combination of above
     IMO, rather not, this overloads the letter, and allows to diverge into a question, which is easy to answer, while ignoring the other ones.
  5. Demanding any of these points, instead of asking kindly, will probably raise the chance of no reply to 100%, but OTOH the wording shall not be too soft, because the "ancient Qt issue" has become a serious and strategic one, technically and WRT licensing, by Jolla not addressing it for years and "the Qt company" winding up their licensing scheme repeatedly.
  6. Something else to conclude with?

• Other ideas?