Split grip isn't dangerous per se – it's more about having your weight supported by muscles that aren't really equipped for it. Any time you are on the pole and have a lot of body weight being supported from underneath by one arm, you are at serious risk for muscle strains – been there, done that myself!
If at any point you are gripping the pole with your bottom hand thumb-down (whether in a carousel, boomerang, cradle, aysha, butterfly, whatever) the main job for the bottom hand is balance and steering – most of your weight should always be taken by the top hand.
This can get tricky with elbow grip aysha because you need to take all your weight while gripping with an elbow. I find that the further I get my hips from the pole, the less pressure I put on my bottom hand, and the safer it is. This could be a problem for straddling down from an aysha – because I don't know off-hand if it's possible to take most of the weight with your elbow grip for the whole descent.
I think you'd either have to focus on keeping the feeling of "leaning out" and pulling away from the pole the whole time or build up a lot of strength in your forearms (as in, more than is natural and it would take some time and work).
Also, I suspect you'd need to be able to hold an "embrace" pose, or better yet a one-handed "embrace" to know that your elbow grip is secure enough to take most of your weight and protect your bottom hand.
I find my upright split grip is most secure when I have my top forearm parallel to the pole: maybe you could try changing your grip to a forearm grip (descend into flag), or split grip with forearm against pole as you descend?
Elbow grip aysha, straddle down sounds like an awesome move. I'll have to see if I can do it. In the meantime take care of yourself and give your poor forearms a rest (easier said than done in my experience!)