Never say never.
In the Northwest (you might now, Ken) there's been a "NASA-like" racing club for decades - the International Conference of Sports Car Clubs (ICSCC or Conference). It was started by a splinter group of disgruntled NW Region SCCA members so was born of ill feelings that just kept on being negative, in both directions.
There were always a few who crossed lines and did events with both clubs but at one point, it happened that we had guys in high places in each, who were friendly. Our RE at the time was one of them and he came up with the idea of the Seattle Cup - a championship for classes common to both organizations, at all of one season's races at Seattle International Raceway (now Pacific Raceways).
As I recall, the clubs split the cost of trophies and someone volunteered to keep track of points. Each club did its own deal but the effort generated some more crossover, some friendly rivalry, and a little goodwill. It wasn't a big deal and was, in a way, the best possible compromise. Nobody had to give anything up so there were no real issues to hassle over.
The next logical extension of this would be to have those who want championship points to register and run the required series and sponsor graphic package. I obviously don't know how USERA is chartered but it wouldn't surprise me if there weren't a way to collaborate on an established NASA enduro.
How about the 25 hours at Thunderhill, hmmm??
K