Ubuntu-ARM will run on the Pandora, no problems whatsoever. We can take the kernel from the official Angstrom distro for the Pandora, and use it to boot a full-blown Ubuntu ARM system, no sweat. No hassle, no fuss. This has already been demo'ed on the Touchbook, which shares the same hardware (and kernel) as the Pandora.
The question is whether or not the advantages of running Ubuntu ARM are going to be feasible on the Angstrom OS that will be shipped from the factory - namely, *a fully working software repository* for updates to the OS? In Ubuntu, you can get used to seeing updates on a consistent basis, and they generally do not interrupt the operational capability of your device - generally.
However, with Angstrom, too many OS distributors just build a custom Angstrom release for their devices, and forget about the repo stage, meaning that if you do updates to the installed base, you typically only get to use the 'official Angstrom repo', which contains safe stuff and nothing at all optimized for the hardware in front of you - in fact, depending on the 'official Angstrom repo' for OS updates is dangerous and not recommended, because things break, and break hard, when there is no repo geared for the decisions made about the Angstrom you are building. Such things as ARM v5 versus ARM v7 compatibility is an issue, for example, and different libs for different platforms being mixed up and jumbled about.
So, in short, yes Ubuntu ARM is going to be possible, and there are good reasons to use it .. if OP Inc are not going to be responsible for their own Angstrom build repo, and are just going to be lazy and incompetent and say "use the official Angstrom repo for updates", then it won't be long until it becomes a messy tragedy. To avoid that, use Ubuntu ARM, *OR* demand that the official Angstrom OS release comes with a properly configured and set up repo for us all to be pulling base OS updates from .. alas, all indications are that OP Inc have no desire to do this, and will just have to suffer from the consequences of a few hundred users doing updates from the 'official' (broken) Angstrom OS repo and getting everything all screwed up ..
DISCLAIMER: my point of view comes from years of experience with completely borked releases of Angstrom/OpenEmbedded distributions for multiple devices. There is only one way to keep the Pandora OS functional: total responsibility in the form of a properly configured and maintained/updated release OS repository, coming from an authoritative source. If this doesn't come from OP Inc, we in the community need to be prepared to deliver it, Open2X style ..