Looks like this project is still on the go with new funding announced today.
"The chancellor is also set to announce £30m in funding towards a rail testing complex in south Wales, located at the Nant Helen surface mine and Onllwyn coal washery at the head of the Dulais and Tawe valleys.
The Welsh Government had estimated the project would cost about £150m, and the Treasury say they will "match fund" up to £30m with the remaining £128m from the Welsh Government and private sector investment."
https://www.bbc.co.uk/news/uk-wales-48201728