I think the most sensible solution would be to store the "othertags" in a separate table as key/value pairs and with a foreign key pointing back to the main table entry.

You could use a StringSearcher or a small Python script to split up the "othertags" to key value pairs.If your data doesn't have a unique global ID, you can create on using the Counter.

The othertags table could e.g.look like this:

osm_id	key	value
1	surface	asphalt
1	name	Ermine Street
1	maxspeed	70