The thing is that while coal plants are tied to coal and can't reasonably be adapted to other fuel sources, gas plants can be adapted to anything that burns - which includes CO2-neutral gas such as methane from biowaste, or methane made from electrolysis H2.
Therefore it is very viable to build gas plants now, especially for peak demand.
There is nothing which stops you converting from coal to natural gas. Plenty of coal plants have it or are in the process. Coal power plants pulverise coal until it is so small that it can be picked up in hot air and blown into the furnace. The already usually use oil or gas to initially warm the furnace.
Therefore it is very viable to build gas plants now, especially for peak demand.