A $149 Switch TV is definitely possible - the entire NVIDIA system-on-chip, including the 4GB of RAM, is maybe ~$40 to make. So you take aware the LCD touchscreen and even double the storage to 64GB - throw in a Switch Pro controller - and yes $149 would still give them a healthy profit margin. But I don't think that's it...
Instead it has to be a Switch Pro (or Super Switch as I really hope Nintendo calls it and others suggested). Another die-shrink of the NVIDIA SoC to 7-nm and double the RAM to 8GB (so, half as much as PS5/Xbox Series X is expected to have, but same as PS4/Xbox One) would make for a very powerful handheld. It would work no differently than PS4>PS4 Pro; all Switch games work on all systems, but can run at higher resolutions/better textures/shadows/etc on Switch Pro. This would be extremely easy for developers because they already always target two different power profiles now - docked and undocked. This would just be adding in two more - Super-speed docked and Super-speed undocked (made up terms on my part lol but you get what I'm saying).
Nintendo's new lineup for Holiday 2020 then could look as such:
$199 Switch Lite
$399 Switch Pro