Two 4.3 mile (7km) electrified tracks for testing trains would loop around a site roughly the size of Gibraltar.
With other facilities, GCRE said it could create more than 1,000 jobs.
It was supposed to be up and running in 2025, but has been delayed until 2030.
The scheme was inherited by Plaid Cymru when it won the Senedd election in May.
GCRE chief executive Simon Jones said there was demand in the rail industry for the services the company would provide “but we can’t carry on using public money on this forever so a decision needs to be made”.
Jones added that there had been “detailed conversations” with an energy and data centre company, but said he could not name it due to commercial confidentiality.
GCRE wants to complete those talks this year so a contract can be signed.
“And we need to be in a position where we know whether the railway is going ahead or not at the moment we sign that contract,” he told Politics Wales.
“If the government decides this is something that it wants to do, if we are able to execute the contract with the data centre partner, then five years from now we could be in a situation where we see trains running around this site.”