Re: on-demand pricing is bullshit
"not the backing store any professional should use for a reliable web service" Horses for courses. My idea of a professional is someone who can work within the constraints that exist.
Your mind is made-up, but you can indeed replicate SQLite with commercial and FOSS packages: Dqlite - https://dqlite.io (If you don't mind using Canonical); rqlite - https://github.com/rqlite/rqlite ; SymmetricDS (but more for replicating to bigger databases) ; aergolite - https://github.com/aergoio/aergolite (I have no idea if it's any good) ; LiteSync - http://litesync.io/en/sqlite-synchronization.html (seems to be pricey).
You can advise that something is not suitable for purpose, and if that is not accepted walk away. I was offered a full time government job to create a Lab Information System. The boss, and a panel, asked for a solution to run across 5 laboratories in different parts of the country - My response, based on writing almost identical systems from scratch, and also installing commercial systems was: Either write their own, and staff it appropriately to look after changes and maintenance themselves; or, buy a commercial system and adapt their operation to match it, and not to install their own custom stuff. Experience had shown that once you move away from a "standard" commercial system with your own modifications, future updates would strand you - They wanted to use their in-house skills which were dBase/Clipper for a front-end (It was the early 90s and dBase was approaching obsolescence) and somehow cobble it onto a new commercial Oracle system - I politely told them "No". They offered me a full-time job at deputy director level (Formal interview panels - Apparently they had heard of them), I said no. They asked why - I told them that in my professional opinion their stuff would be orphaned by the commercial supplier. They asked for other alternatives. I thought that as they (like almost all labs) were using spreadsheets extensively, they could continue to use them for local manipulation and display, provided that all of the results were secured and available through a database; and that they should invest in a decent report writer (Not Crystal!) for printed output. They still wanted dBase and Oracle, and seemed to not understand why I wouldn't take a nice government job (I'd been a Scientific Civil Servant before my last salaried job). They went ahead with someone else who was a general programmer. It was a disaster, and after struggling for a few years, his successor installed an off-the-peg commercial system.
I see from your posts that you use Python. I use and like it too, but for heavy lifting on a server I would use it with C (My age is showing, maybe you would like C++). SQLite was originally written to do some quite serious stuff in Tcl and C, including talking to "real" databases. That's why I liked it with PostgreSQL for some of our commercial stuff (As you know great for prototyping, but we realised that it worked well for a lot of stuff by itself). My customer base is probably different - We specialized in $2-20 million p.a. companies, as well as local authorities and smaller government departments. A big database for them increased by "only" 10,000 - 10,000,000 rows p.a., but the data was "important to them, and needed to be right" - Much of the database didn't need to be live, so historical storage in read-only archived tables was preferable (UNION SELECT or UNION virtual table with the live stuff).
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OK, some rambling old-fart lessons learned in 50 years of doing this sort of stuff:-
Work for yourself, you'll never be rich or secure as an employee or contractor. If it all goes wrong it's your own fault.
Keep up (highly) specialist skills outside IT, otherwise your work gets outsourced cheaply to someone with generic skills. I'm a Chartered Chemist - Someone told me about 40 years ago that it's relatively easy for a chemist to get IT skills, but not for an IT person to do chemistry - I cheated, I needed to do this stuff in the 1970/80s for chemistry, but a lot of paying work was outside that.
Soft skills are nearly as important as technical nowse. If you can't get on with people you are wasting your and their time.
Microsoft has persuaded most that "only just" good enough is good enough. Computing stuff not working seems to be tolerated by many: Yesterday I was "helping" a younger neighbour to order coffee. The Nespresso web site and App were down for at least an hour, she thought that this was normal. I prefer stuff that works (within the punter's constraints).
Avoid commercial (database) packages whenever possible: Oracle - What do you call an Oracle Customer? A Hostage... Microsoft - That's a lot of SQL Server instances/databases you have there - Congratulations, we have just dramatically changed our licencing (Sorry, it's much more expensive)...
Cheers.