The code may be old, but I have never seen a forum as fast, stable and secure as YAF in the last decade. Most known softwares I have seen had so many problems that a lot of servers were forced do migrate to different products with a lot of time spent in the process.
What is the best alternative to YAF, now? I do not even know, I have had enough with security problems, urgent updates, frequent "optional" (but in reality "mandatory") paid updates to consider a move. Even if I could find a better product, how long would it stay with us? Forums are not tiny phone apps, they last for years and years, users get accustomed to them and changing is a good move only if it gives BIG improvements.
So, in my opinion, radically changing architecture in a free software to satisfy the needs of a user who has his own developers to make their job easier is not an option tha_watcha should consider being the only remaining developer. Real job, family, friends, etc... ARE important.
Raising funds to aid further developement of this platform is an interesting option I would subscribe, but does the_watcha have even the time to organize a poll to decide which functions should be up on the list? Could he find anybody to help out with code? I believe he could, and I wish this project will continue, but I do not think it is fair to push him towards this.
My personal opinion: I *really* think that if he could devote a couple of hours a day to help new developers these could be found, helped by a small fund raising among YAF users who would be happy to pay for new functions or remote assistance, as in many open source projects out there. Make a living from open source is hard, but not impossible, this is why this kind of project has frequent changes in staff. Now, the_watcha is alone and I sincerely hope he will not give up on the project which is still very promising, only needs to be revived.
We have to remember that he did a great job solving almost every bug users found in this software, which is now excellent.
Not many new functions are necessary, but one thing is really in need of improvement: mobile version. Be it responsive design or another solution, nowadays the most of visitors come from mobile platform and YAF is not up to date in this regard.
I really do not understand admins who ask for fancy new functions forgetting the most of their users have a non-optimal experience when browsing YAF from tablets and smartphones, that is to say for the MAJORITY of their time on the forums!
So, the_watcha, a big thank you for all you have done, but do not give up now on further developement: YAF is one step only from a perfect forum, just mobile functions should be updated. Stop bug checking, write a new "to do" list, ask for help by new developers and start a fund raising. I am in!