Sometimes you just need a real debugger. Wouldn’t it be wonderful during early development to have J-Teensy variations, otherwise similar to the existing USB-boot MCUs, sporting a JTAG port for boot/debug.
Sure… it’s just always a balance of the additional component cost vs the value add for the customer vs the increased price
I know you’re after a ready-made version, but if you’re in a pinch I have seen folks use an external JTAG with teensy