OK - first of all, the Windows Client Code will never be supported under Linux - there are way too many Windows calls for Peoplesoft to port, and it is incredibly unlikely they will re-commit to the Java client again.
However, the JAS server, as I mentioned before, already works perfectly well under Linux - and I am using FreeBSD and Redhat successfully with this for development and testing purposes - even though it is many times faster than other platforms.
As for Database support - JDE only recently introduced support for UDB (a couple of years back) and this customer base has increased, albeit relatively slowly. The push towards Linux has come from the IBM camp, so the initial support for a Linux Logic Server will be on UDB (but obviously, Oracle will work perfectly well as well - just like any other Unix server). MySQL - in my opinion - will not be supported for several years. The reason for this is because although MySQL has improved dramatically in the last couple of years, it is still considered in the software industry from being far from a massively multi-user database architecture in the same vein as Oracle, DB2 or Microsoft SQL Server. It operates very competitively against MS Access - but other opensource database engines are much better architected including PostgressSQL. Peoplesoft will unlikely support anything but a "mainstream" database - and although MySQL is being used by everyone for Database Access on websites - the size of these databases are usually miniscual when compared to an ERP database.
More work in the community with MySQL would have to be completeted to raise its scalability in this effort - especially with network interfaces (such as OCI and ODBC).
Linux support was only announced VERY recently. I do not expect to see Linux support in the product until towards the end of this year with ERP 8.9 Service Pack 3 (23 on Xe/8.0) - and likely support will only start with 8.10 customers.
Of course, although I "dabble" and deploy within development and test environments - I wouldn't deploy into production until I had confirmation that someone had beaten me to the punch ! Never be a "guineapig" I always say !