Split key is optional - some people do not know how to use a split key, that was my initial concern.
Make a tutorial. It's not hard. Maybe put some images and you're done.
Example:
1. Go to Bitaddress.org (optionally download its source code on
https://github.com/pointbiz/bitaddress.org/archive/v3.3.0.zip) and open it;
2. Move your mouse around until 100%;
3. Click on the "Vanity Wallet" tab;
4. Click on "Generate" and don't close the tab;
5. Paste the "Step 1 Public Key" in the generator's split-key field and click "Generate Address";
6. Meanwhile, go back to bitaddress and paste the "Step 1 Private Key" into bitaddress' first box;
7. When the service finds the address, paste the generator's "BTC Privkey part" into Bitaddress' second box;
8. Click "Calculate Vanity Wallet";
9. It should show your vanity address private-key.
I will not be forcing split key, because of usability and accessibility
Stop giving excuses. Make your service truly secure.
Security > Usability. Otherwise, we should just use Coinbase.