As far as I know, the now running version is the last one I could upgrade to without having to rewrite the hole configuration from scratch, because of incompatibilities.
This is usually not that hard to do, and is far better than using a version that has many known security vulnerabilities. Consider that this is the device responsible for protecting your network - you should aim to make it as secure as reasonably possible.
Because there is no one size fits all solution for network design. A nearly infinite number of variations make it really hard to script a generic conversion. Instead of spending tons of time trying to automate the process, people simply migrate their devices manually. It is a one time deal.
…every user is forced to spend tons of time trying to migrate…
…and make no mistakes that forces them to repeat the process over and over again.
Excuse me, I am not trying to bully you or any developer, but it always hits my nerves when some one provides a “better version” of this or a “more sophisticated version” of that, and leaving the troubles of the migration process entirely to the users. This is not just an IT thing. If you threw a new type of car onto the market, where you’d have to pull the gas pedal towards you for breaking, because it’d look and feel much more “state of the art” and it also would save one pedal in the production chain, and then you’d tell people “Well, you just have to adjust to this new kind of driving!”, what do you think how long and well this car would sell? How much would people like to drive it?
It is my believe that every one offering some “new” techniques to the public should not forget those users that already use the “old” technique and tell them to get along with it on their own or just die silently.
Once again: if it isn’t “that hard to do”, what kept the authors of OpenWRT apps from including a small routing in their apps to read old configuration and write out as new configuration style? Is it better for one person making life easier for many uses, or many users having to fulfil the specifications and regulations given by one person?
As a famous Vulcan science officer once said: “The needs of the many outweigh the needs of the few.”
That is my opinion, I do not expect you to share it.
Then you need to do that, first - especially if you're asking others for their support.
Apart from the mix-up between fact and fiction, "because the needs of the one… outweigh the needs of the many." - especially if no one has managed to write this mystical conversion script you imply to be so easy within the last 8 years. Your device and running firmware will just get older and even more insecure, nothing will magically fix your configuration. swconfig has never been accepted to the mainline kernel (on the contrary, it has be actively rejected), DSA has - so perhaps re-evaluate who the few- and who the many are.