Consumer apps and development platforms have very different needs.
If a consumer app stops working, it inconveniences the user.
If a development platform stops working, it causes material harm to an entire downstream ecosystem.
For this reason, attracting new developers to a platform will depend on the ability to demonstrate sustainability.
That is precisely the reason behind my focus on funding.2. 'self-sustaining' . . .
Dunno what that means. Software is never 'self-sustaining'; either someone keeps developing it or they don't: it certainly does NOT do it by itself.
If by "commercial version" you mean the proprietary product produced by another entity, what separate orgs do may inform one another but carry no obligations either way.3. 'in a business sense' . . .
Even though the LiveCode community codebase is open source, someone could (as far as I know) charge money for an IDE based on it [although they would have to make their variant code-base freely available], and that could be at a price that would undercut the commercial version...
As a practical matter, however, paywalling open source rarely helps. The license openly encourages sharing. So while the license expresses no opinion on fees, as a practical matter a single sale would be all that's needed to spawn a fork which could then be shared at any price, or none at all.
For this reason, most successful open source projects rely on grants, donations, and service work rather than usage fees.
Yes, most have at least some salaried staff, but the income to cover payroll comes from donations, grants, and services, rather than usage fees.4. GIMP / Inkscape / LibreOffice / Mozilla
How much these applications are dependent on paid income (rather than donations) is not clear to me. However, unlike what I outlined above, they do have paid employees.
Yes, it is, a scale which aims beyond limping along to keep legacy scripts alive for a couple years, to seek new audiences using the technology to build new things.5. 'self-sustaining' . . .
If by that you mean some sort of 'LC 963 Community Continuation' foundation [pace LibreOffice], that's a whole different thing in terms of organisation and scale.
We seem to share an awareness of the critical need for funding to employ the C++ experts needed to fulfill the mission.I am not at all sure why something like that should be necessary
A nonprofit foundation would provide a means for donations made to support the project to be tax-deductible. If you've served on the board for a nonprofit, you know how important that is for attracting donations, esp from institutions.