Every single MongoDB step has had the old timers groaning.
Even with something solid like Tokutek's storage engine in it, its going to be a hard sell.
I'm confused by your comment. The beginning acknowledges the fact that MongoDB has a weak storage engine, but your conclusion is that, even with a strong storage engine like ours, there is still a problem. What other problems do you see? Are they something we could work on?
The problem is that Mongo advertised itself as a database and wasn't one. Once you do that reputation of the product is dead forever.
TokuMX is a real database as far as I can see, MVCC, great indexing story etc.
By association TokuMX is probably not regarded as highly as it should be. Which is a shame but it's a people problem, not a technical one. People can very easily lose trust in a technology at which point it's effectively dead, it might take a long time to die due to lock-in but it's dead.
For instance I have recently started playing with RethinkDB over TokuMX almost purely because of Mongo association.
Now technically that might not sound like good reasoning but when you think about the kind of person that writes a database that doesn't fsync your writes by default and relies on the page-cache over doing direct I/O when building a database.. doesn't really inspire confidence in the network stack, the query planner.. or well anything.
If anything it makes you insistent on not having ANYTHING to do with that sort of codebase.
Just replacing the storage engine might actually be good enough, but restoring my trust in the rest of the codebase is almost a forgone conclusion at this point.
They can try and rewrite the web and remove all the silly benchmarks, but they were the loudest "web scale" cowboys back in the beginning and we remember them for it.
I disagree with them on what is the minimum viable product for a database. I come a storage and service provider background where failures are treated very harshly (usually death of companies for singular mistakes) so I take releasing a product that stores customer data very seriously.
To be honest this is the biggest attraction for me to RethinkDB. They waited a sufficiently long amount of time with a commercially backed team of very competent engineers that obviously have the required background to sit down and DESIGN a database. The query language generates a non-turing complete language with a clean AST the has all the right deterministic characteristics to implement a powerful planner/optimizer. Their on disk format has been abit in flux but the core design is excellent and you can see that it has been optimized for very fast range queries. Even the API protocol and serialization were designed with care, not to mention the excellent ReQL language and attention to detail when integrating drivers into the host language.
Which is the other thing I tend to dislike about Mongo, it reeks of lack of design. The journalling effort for instance as you pointed out is very adhoc, this goes for GridFS and alot of the other features they have integrated into the codebase. These are smells that I can't ignore when looking at a product that I need to trust with my data.
The counter argument is to not trust it with your data. But I am yet to find a reason where that makes sense where another datastore wouldn't be a better choice.