Well, as basic toolchain, any MIPS32 compiler and the GNU libraries available from Philips is probably good enough for a start, but I see difficulties in getting data&driver on the available HW accelerators (the PNX5xxx), as well as actually getting the application in the TV and starting/hooking it into Jointspace.
I just looked into Jointspace a little more, and must say, I'm impressed! (see
here or
here if you're interested). So, Philips recognized this problem of software architecures and development a few years ago already and works to solve it :-) It seems Jointspace offers the flexibility and stability to outsource respective components.
I don't fully understand the architecture (esp. the role of the applicationManager and what's possible / not possible in hooking in new applications), but I think there is a huge potential in such an architecture - especially as it is not closed, but documented and publicly available.
Philips can get in the independent developer & open-source community, for remote applications, they actually already doing this.
Not sure about this, but my guess is, Jointspace is already used for the "on-tv" apps, so this is a hook we could use. So, if Philips wanted to go the next step and and provide the possibility to run cross-compiled jointspace applications directly on the TV (e.g. from USB, maybe even in a chroot environment for security) and hook them into the home menu, or capture and re-assign keys to replace existing applications, that would offer the possibility to include/improve TV applications.
Of course, this doesn't allow to fix bugs, such as the media player sorting, unless Phlips would provide the source-code or library API for these applications.
But it would provide the possibility to build a new image viewer application - even if it would mean re-implementing the DNLA interface.
Or a video player could be developed that supports more formats (e.g. based on mplayer) - even if a lot of effort would need to go into optimizing it for the platform.
Maybe, things like the automated EPG could even be implemented now over the remote jointspace interface, but it would a PC of it's own to run the application, this is why a way to run applications on the PNX itself would be really cool.
Well, Philips made a first step of publishing the Jointspace architecture - maybe more step in running "local" applications will hopefully follow :-)