What makes it even more odd is that there is a real wealth of good quality information on (and applications for) Seipai available to karateka. This is not just a recent phenomenon, way back in 1934, Mabuni Kenwa shinshii wrote Seipai no Kenkyu (Study of Seipai). This book contains interesting insights on kata generally as well as some bunkai which go beyond the modern percussive "punch/block" karate so common in the 20th century including a few tuidi type techniques.
The original Japanese text can be downloaded here
A whole host of interesting YouTube clips exist. Let's start with Ian Abernethy (who's karate in these clips is uncharacteristically Okinawan in feel):
OK, that wasn't bad, both rational and practical... but lets kick it up a few notches and look at Taira Masaji shinshii doing some Seipai material:
Now a couple of his student Andrea Buttazzoni shinshii who is an impressive karateka is his own right.
Here is Garry Lever shinshii of the Shinsokai working Seipai waza on a wooden man dummy (tou).
Finally let's look at some more tuidi concepts and techniques based on the movements of Seipai
This one is from Dan Djurdjevic shinshii:
And another from Jesse Enkamp of KARATEbyJesse fame: