Node, Redis, Mongo are all still in use (although Redis pub/sub no longer is). There are a lot more components, though, and some of the front-end libraries listed are no longer true.
Did you use it with other people? While it can work on an individual level (i.e. where you are just making boards for yourself), that isn't really what it was designed for. I wouldn't put it in the same group of tools as personal productivity software. While you can use it for yourself, it really shines when you have a group of people trying to collaborate and share information.
It's especially useful for viewers (i.e. not people writing things in Trello, but people watching others update info and tracking the progress of something).
Fog Creek employees keep on making Fog Creek awesome, and yes, they have a stake in Trello Inc. (Some of the longstanding employees now even have a stake in both Stack Exchange AND Trello).
We won't disclose that info because it just invites a bunch of unwanted discussion about valuations. It's probably not too difficult to make an educated guess.
I don't agree with what you wrote at the end. It's not a "mistake" to bootstrap and have a much higher probability of success with a lower possible return. I know that's probably not what you meant, because you wrote earlier that we could have been "more successful", but it also ignores what would have been a much higher risk and loss of ownership in your assumption.
Joel and I are naturally conservative in nature and having succeeded at Fog Creek with what we set out to do (building a successful company where devs wanted to work) allowed us to swing for the fences with Trello and Stack Exchange. The risk is much higher. The reward is bigger, but we own a lot less of those VC funded companies.
I know that for some people, this is an issue. The problem is the cost of switching to another name. For a ten year old product, the cost is IMMENSE. It can definitely be done, but it's a hard problem.
Naming is also really hard. We spent TONS of time picking out the name Trello and just narrowly avoided naming it something really stupid by serendipity. (The code name was Trellis, but all the domains were taken and we insisted on having a dotcom url).
We also have no plans to make an in-house solution. While the tide has not 100% turned, in most places at big companies like Amazon and Microsoft, they can already use SaaS solutions (you sign a big contract, but even if your app is on AWS, msft employees can use it). For the companies that cannot, the added complexity to development and support is likely not worth it (for us).
Somewhat off-topic, but on https://trello.com/enterprise, you say that you provide "24 x 7 x 365 incidence response" where I think you mean "24 x 7 x 365 incident response".
Since a business closing does not typically occur in week-long increments, probably not. "24 x 7 x 364" is generally understood to mean one day off a year (usually Christmas Day in the US), and "24 x 7 x 51" would not be clear at all.
But I think the more interesting link for the HN crowd is this one:
How to build a Trello powerup: https://developers.trello.com/power-ups/samples
Sample github repo: https://github.com/trello/power-up-template