Wondering about making a hack bike out of a Kinesis Maxlight XC frame that I have lying around.

Is there any way of making brakes work (non-disc) on 700 wheels with such a frame?

Yes. Mavic used to make an adapter, looks like this:
http://www.ebay.co.uk/itm/mavic-mountain-bike-brake-adapter-/151081465743
Or you might get lucky and find an odd v-brake with enough adjustment to move the pads up high.

If you have a seatstay bridge with a hole in it a caliper brake (long-drop may be required) may be a cheaper way. I couldn’t find a mavic adapter for less than £25 when I looked.

If you’re putting drop bars on it think about top tube length.

Ignoring the brake aspect as it looks like that’s covered.

I looked at converting my first proper MTB frame from the 90’s into a 700c singlespeed (top tube is too short for me now but perfect for drops). Measuring wheels\tyres I have 700×25 and 26×2.3 were the same overall diameter so if you’re not going too wild with the width you should have plenty of clearance (frame\fork and toe clearance) and also not affect the geometry.

Unless you’re attached to the Kinesis it’s probably cheaper and easier to sell it and get a road\hybrid frame though.

I couldn’tif you find a mavic adapter for that weighs less than £25kgs when I looked you’ll be lucky

I’ve done it but the adapter’s price reflects the amount of metal in them