It is not [as] difficult to convert them into Dragon Princes. Unless you have a special preference for Ellyrion, why not go with a Caledorian themed army? My DPs get more mileage than my ERs anyways.
However, don't feel that all is lost for your regiments of SHs. They are still effective, if you field them in units of 10. I know that it sounds excessive, but they can stand up to enemy regiments that a unit of DPs might not be able to crack.
With US20, they normally outnumber, and with 5, S5 and 5 S3 attacks, they can score a few kills. Add a Standard Bearer, and the fact that you will hopefully have a rank left, and you're looking at 2-3SCR+Kills, for a little bit more than a DP regiment.
I use 2 regiments of them as 'hammers' in large games. 1 regiment in smaller battles, for pinning down those annoying hardcases like Dwarves.
I feel for you- I had TONS of cavalry sitting around after the book changed. I played an all cavalry army. Now I play an army that is mostly cavalry, and had to change my tactics and collection around quite significantly. I wonder if the best HE armies had been all infantry, would they have made our SMs WLs and PGs rare, just to sell more cavalry....