WFC has indicated in the past about its desire to fill holes in its coverage and expand into Kansas and Missouri. WFC doesn't have significant retail banking operations in either St. Louis or Kansas City. There are are only two potential targets left --- CBSH and UMBF now that FSR has purchased Mercantile. Both CBSH and UMBF are controlled by different factions of the Kemper family. Neither faction has been very interested in selling in the past. WFC is a first class operation and trades at 3.2x book. WFC could easily pay a good premium for either UMBF or CBSH if (big IF) either ever wanted to sell.
Just my opinion.
Full disclosure: I own long positions in both UMBF and CBSH