Long term storage has the simple economic challenge that it's simply redundant most of the time and therefore very expensive for the few times it might actually be needed. As a result, alternatives to storage tend to be more economical and practical. Having gas as a backup is a given for the next few decades. There are so many gas plants around and more are being built. Mostly short term storage is actually marginalizing a lot of those in their role as peaker-plants.
The plan for the last few percent of the renewable transition, which is what long term storage would be about is a lot less interesting than just getting the first 90-95% out of the way. Which will work fine without anything complicated or new. Burning some gas for the remaining percentages is not pretty as a stop gap solution but it's a lot better than what we currently do. We have a 3-5 decades to figure out the rest.
Towards the end of that period, most remaining gas plants will be running less and less. There are a lot of other solutions than long term storage btw. Including using cables to move power around over long distances. Connect sunny areas to dark areas. Or windy areas to calm areas. There are some plans in various stages of progress to connect e.g. Singapore with Australia, Morocco with the UK, the east coast of Canada with Europe, etc. Each of those projects adds many GW of power import and export capability. Add things like flexible demand to the mix and we gain the ability to turn things on/off selectively depending on power availability.