However, I build wooden kayaks as a hobby and often mix up batches of epoxy thickened with wood flour. Anybody used thickened epoxy for fill binding holes? Anybody see a problem with doing so?
If you're talking of flowable-type epoxy and thickening it to peanut-butter consistency like one does to make fillets in stitch-n-glue construction, then no, there is not a problem; you could alternatively use a fine silica thickener and it would flow better. Flow both better out of a glue syringe and better into a hole.
Most of the epoxies I see talked of here (meaning on this forum, e.g. Devcon, Hysol) are designed for ease of use and a relatively fast cure time. The type you're talking about requires a bit of *ahem* commitment, in terms of up-front cost, in terms of learning to use the product and in terms of the steps involved with each application. If you do decide to use silica thickener, you'd effectively be creating something very like a product known here as PC7/PC11 marine epoxy.