There are a lot of difficult trade-offs to make. Another consistent feedback is the 3.5 and 3.6 boards are physically too large for some projects. Sure, many people prototype on breadboards, but then they often put it all inside something else.
Cost is also a big issue, especially compared to ESP and Raspberry Pi. Aside from the cost of parts, keeping all the hardware the same is the biggest factor. Offering different options divides the manufacturing batch sizes, which drives up the costs, and it becomes much less realistic for distributors to carry. It’s easy to imagine adding more models from only a technical perspective, but that’s only half of the story. To make Teensy work long term, the business model has to be realistic, which is increasingly difficult in a market flooded with subsidized products (Pi Zero) and ESP modules, and of course Chinese clones.
But I am considering something like this, likely smaller, probably more focused on a specific purpose like an 8 bit TFT. There are still many choices to be made. Just please understand we’ve been down this discussion many times before. The combination of engineering trade offs and economic reality of a fully independent dev board (not financed by any big semiconductor company) means not everything that can be imagined actually is practical.