While I do hope they will have more available then the NES classic, I'm not holding my breath. This isn't Nintendo's main revenue stream and they are not going to risk the Switch, which is currently having it own issues with part supplies. You have to remember that Nintendo doesn't have its own manufacturing it has to lease space from other companies and if the demand out paces the supply there isn't very much they can do to increase it in an expeditious manner.
Plus contract runs out and usually factories that do contract work schedule ahead with what they are going to do next, so extensions while possible will be treated as low priority since they already have another contract. So if Nintendo wants to continue to use the lines need to make a deal with the next contract holder, which will drive up costs for them. (Which is probably one of the reasons the NES classic was finally scrapped because the costs out weighed the profits.)
These are treated as limited time collectors items and as such there is almost always a secondary market and the prices are horrible. Think about the Ty Bennie Baby happy meal toys. $1.00 to buy from a McDonalds at the time, hundreds to buy from ebay at times. It just the nature of the market.