(admins, please feel free to correct me on my assessment and assumptions)
From my observation, LYN runs on a very rare version of Invision Power Board (IPB) software. It's an early release of IPB 2.x.x which is although it is marked as 'Trial' (as you can see from the board's footer), it doesnt have any limitations (as in time expiry or posts limitations) attached to it. If I'm not mistaken, this is the PF release of IPB 2.0.0. This version has been discontinued by Invision and was replaced with newer Trial version that carried some limitations. In essence, LYN doesn't have to pay for licensing fees as it is running on Trial and the Trial version that LYN has does not have any imposed limitations, thus making it as good and stable as the full version of IPB 2.0.0. The only catch is that this Trial version cannot get official updates and patches from Invision. Besides that, LYN cannot remove the 'Trial' signature and linkback to Invision's website on the board's footer.

As there are no official updates from Invision, any fixes and patches are carried out manually by LYN's admins which I must say is quite an incredible feat seeing that LYN is still running strong to this day. From the point of release which was in 2004 until now (2010), I'm certain that there have been a large number of fixes and adjustments done to the board by the admins. So much so that what's under the hood of the current LYN board no longer resembles the initial release of its original IPB version. Hence, it's safe to assume that LYN has been highly customized over time to cope with the patches and fixes, and also the adjustments to fit LYN community needs and requests. As such, hypothetically, should Tapatalk decides to release a plug-in for IPB 2.x.x, integrating it into LYN will not be a straight forward process.

That is roughly the main challenge that we'll have to face if we are into making this XDA-like app for LYN. We cant just go out and download a copy of IPB and use it to develop our app. The copy of the IPB must be the exact duplicate as what LYN is using right now. In other words, without LYN admins' blessings, we cannot pull this off. We need to get this issue sorted out first. What I'm trying to avoid is the situation where we poured our time developing the client side of the app (the Java part) and then later finding out that we cannot integrate it to the board as we dont have the admins permission and cooperation to do so. Therefore, IMHO, the first step is to get the LYN's admins involved in this. Without them, I do not see how this thing can go any further.