They already released a normal switch with battery improvement, new soc, new joy cons lol in August 2019 before the switch lite came out.
Why would they re release the same thing again?
To make gradual improvements.
There were rumors last year about a "Switch Pro" and all this pro model had were some modest improvements to the base Switch. I wouldn't be surprised if they do the same thing again.
Except it wasn't a "Pro", it was just the same original Switch with slight improvements. The Pro rumors turned out to be wrong and instead it was just the original Switch getting small internal improvements.. Companies normally do these types of updates, make a slightly more efficient version, usually reduces their cost too, and just swaps out the older model with the new model, usually no one even noticed cuz it's still the same model. It's not a different retail version, its just a small update to the same thing. A "Pro", or whatever, means a new retail item, with significant enhancements over the original and will cost more than whatever the current original Switch's price is when it comes out.
A "Pro" would probably mean improved game performance, larger screen, perhaps another improvement in battery capacity, larger internal storage, and a few small tweaks to the design to make it look like a new item, coming in at a higher price.
As far as a digital only version, I don't think it is very likely at all. A Switch "Pro" or a Switch Home/TV is far more likely. I doubt a digital only Switch would be very popular. I mean I try to pretty much only buy digital, but even I have 5 physical games now. Taking away a big advantage (physical games) wouldn't save a whole lot of money in the design of the system, and I think consumers would see that as a net negative compared to any price reductions. And it wouldn't be much of a price reduction because a digital only version would need a much larger internal storage.
In the end the Switch lineup will likely be Lite, "Pro", OG (if the Pro doesn't just entirely replace this), and maybe a "Home/TV". Lite and Home would have similar pricing at $200 for the foreseeable future, Pro would be $300 and if OG is still around it'd be $250 but honestly I think the OG would just be discontinued like the original 3DS a while after the Pro hit the market.