I guess I don't really see the many problems. I have fallen, and seen others fall, into the "abu za'u re'u cusku" trap and similar traps many times. I don't recall seeing things like "li 827266128281627362816Z" or even like "li R2D2" much in use.
It isn't about how common it is; it is that your proposal will make it such that there aren't any good solutions for arbitrary character strings anymore. Many established and proposed conventions (jo'au*, my proposed date system, Pierre's coordinate system) also depend on arbitrary character strings, often heavy in digits.
* {jo'au}, under my halfway proposal, could be patched by using {mo'e me'o cylyly pa pi'e pa jo'au}
Having to decide when digits can be mixed with letters and when they can't would introduce more usage difficulties in my opinion. I just don't see lerfu-strings being used that much, let alone ones containing digits.
LI...LOhO is the only exception; I don't see what's so difficult to grasp about that.