Here is a list that's been growing on Darkcointalk.org of ideas that we've been coming up with for Masternodes to do for us:
1. send encrypted messages with darksend payments
2. make an escrow trade service that is decentralized (I see this as another type of wallet that might work off fees, where other coin developers would get involved)
3. make some type of exchange between currencies that can be done decentralized from the wallet at an agreed exchange rate between agreeing parties.
4. DACs (decentralised autonomous corporations or communities)
5. CPU miners auto on in QT wallet with auto idle when computer is in use. Possibly run through p2pool as a choice.
6. These cpu miners in the wallet could connect to p2pools by pinging for closest one, via advanced settings.
7. Lightening up the block chain somehow?
8. Give the wallet a notification thing that tells people if there is an updated wallet available or required. BUT LimLims points out this is subject to a single-point-of-failure attack vector
9. A companion program that keeps track of all tax obligations referencing mined coins, bought coins, sold coins, etc... keeping track of current main exchange price at the time of creation, etc...
10. monitor the number of alive master nodes over time, and if it drops dramatically, have a little amber warning light on the send page to communicate that darksend transactions may be less secure (possible DDOS).
11. create a feature of load wallet (.dat file) rather than having to move it to the folder manually? (so you can have several wallets on your machine, easy load)
12. Upgrade to quantum computer resistant algorithms
https://darkcointalk.org/goto/post?id=7134#post-7134 read Alex' post to understand ;P
13. Multi coin wallet (keep BTC and DRK accessible in one wallet)
https://darkcointalk.org/threads/list-of-future-development-ideas.89/