Another idea would be to create a new button altogether for the ‘turbo toggle.’ If someone prefers the old way, they wouldn’t have to do anything, everything would still work the same, but if someone prefers the idea of cycling different turbo speeds, they could specify a ‘turbo toggle’ key, instead of a ‘turbo’ key. Or, you could even set both. Turbo set to L2, and turbo toggle set to L1.
*edit: Just realized you more or less said the same thing, and I misunderstood. 