Though mapleprimes will help you with maple related questions, I will be surprised if you find help for this. In my opinion, Maple's initial goal was to call define_external and build on external routines. They should have just done this instead of rewriting (sometimes wrong) codes for dsolve/numeric, pde/numeric, etc. Perhaps, compiler changes make this complicated, but many commands won't work well for define external (for fortran or C). Though I like maplesim, in my opinion, Maple folks dropped the ball on this after Maplesim came online.
For example, I would like to see RK, or Fortran codes (MEBDF, eg.,) in Fortran and someone explaining how this gets converted to dll files in Maple. If we get help for this (including sparse matrices/vectors), Maple can get very powerful (by calling all possible open-source ODE/DAE/PDE/FEM solvers, optimizers).
Edits: I have learned a lot from the current implementation of ODE/DAE solvers in Maple and the transparent nature of implementation helps in identifying errors when the solvers fail. The same thing can't be said about NLPSolve. It frequently fails for gradient-based inequality constrained optimizations for blackbox objectives. If the plan is to call external routines, implementing them correctly is very important.