The fun thing about math (and science and technology as well) is that it is you can't always tell what is going to useful down the road.
"Interestingness" is often as good a heuristic as any when looking for paths that lead to useful developments, although the path is often not a straight one or short one.
I also like the idea of secondary and tertiary effects. One simple example: By "playing" with cute yet fun ideas that are highly likely to not lead to anything immediately interesting, we can build up skillsets and capabilities that lead to very useful results for other problems. Perhaps this is somewhat akin to how the young of predator species "play" around in a way that prepares them to actually hunt when they are older.
Have any developments come out of adding the digits? My impulse is to dismiss it out of hand because it only works in base-10, which in my mind leans it towards numerology instead of math.
I'm terrible at discrete math so I'm not going to work it out, but I'm sure it would be possible to express that relationship in a way that it could adapt to other number bases, and then it might be easier to tell if there is something there.
(something like treating the digits as coefficients of a series of powers of the number base, defining a function f(b,n) that returns the sum of the digits of n in base b, setting that equal to the product of the forward and reverse representation of that result in base b, and seeing if the equation looks interesting)
E.g. you can use a similar technique to show why the finger counting method of multiplying by 9 works, or why multiples of 3 have digits that sum to a multiple of 3 (same for 9)
I would not be surprised if it is found to be useful. My reason for this is the Quran's mathematical composition, founded on the number 19:
https://www.masjidtucson.org/quran/miracle/
The burden of proof is on the person making the claim. Pray supply something more substantial than a link (to what looks like a religious organisation) in support of your claim.