PE&O do have plans to upgrade the database for apex.oracle.com, but I can't confirm that schedule right now.
Just to clarify things in relation to the versioning - 18.1.0.00.45 is the version of Oracle Application Express. That's not referring to the database version that the product is installed in. As you have seen, the hosted instance is running on 188.8.131.52.0 currently, and presumably that's the version you've also got installed on your VM.
You may not be aware that Oracle XE 18c is scheduled for release soon - see this forum post by the Oracle XE PM, Gerald Venzl: Hello, I'm the new product manager for Oracle Database XE. So once it's available for download from OTN, you'll be able to install our latest production release, APEX 18.1.
I hope this helps.