Appreciate the thoughts.
I was thinking about taking voltage from the input side of the existing BEC circuit, if I was to establish that, would there be any potential pitfalls of using that as my (now switched) input?
I figure there might be some current limitations, given those traces might only be made to cater for the factory 3A, but for a little more info this is on a 1/8 buggy with single servo and RX, and a conscious servo choice (Futaba or Sanwa, where peak current draw seems to be ~2A max at stall) so I think in this particular application that shouldn't be a concern. I really just want the higher voltage since stock is 5.75V.

I'm a little reluctant to go poking around looking for that input voltage, especially if someone else has already figured this out (the ESC has been around for at least 6 years now!). It's a double decker board but I'm pretty sure the BEC reg chip is on the very underside. If I do try to figure it out myself I'll use a minimal power source and perhaps a current limiting device in series, if I find out I'll share here for future reference.

The other relatively neat (and safer) option would be to gut the factory switch and route the actual switch (not setup pushbutton) through a new DPST switch, and use the extra pole to switch the BEC.

Open to further thoughts or suggestions.