I asked about Vox support a month ago and have heard nothing. When the Arc was announced they made some noises about still supporting the Vox but it seems its dead to them. Don't be surprised if the Arc goes the same way.
To be fair though its not as though abandonment of slightly older products is exclusive to Kobo otherwise where's the incentive to buy the newer hardware.
I get the impression Samsung and the Nexus devices get better long term support. For unofficial support (i.e. android updates) best have a look at the xda forums and see what tablets are being worked on.