I'm considering using OpenWrt on a Linksys for a couple of projects.

In addition to the router's normal functions, I'll need it to read several I2C/I2S devices periodically via the GPIO lines, and transmit the results via wireless.  Ideally, I'd like to poll these devices approximately every 33ms.

Is this possible?

True "real-time" performance isn't required.  Constant jitter in the measurement time of 10ms or less is fine; and so are larger errors, as long as they're infrequent.  The router will not be heavily loaded while measurements are being taken.  Time between measurement, transmission, and receipt of data is also not an issue.