They may as well just leave them as they are. I think someone said on the show last night it was a 32 day series. Since that was said on Day 10, I'd imagine that it's actually a 31 day series, and show ends on Feb 6th.
With that in mind, they have 5 more eviction nights (assuming they evict someone on Tue/Wed, and then someone on Friday) with 11 housemates left. Assuming there's no double evictions, that leaves 6 in the final, which is the number they seem to like these days. The show doesn't really NEED a new housemate to spice it up - they didn't even need Pricey. I'd rather them save people for the summer CBB, and keep this lot as they are.