The other major thing I have heard is that in order to get LEDs to projector gobos, they have to be bounced off of glass mirrors or something like that. This would also cause a loss of light. So I don't think it will out put like an arc lamp any time soon. Optic trains on arc lamps just keep getting better and better. The other major thing lamp companies will have to look at is they will never have the sales like they do now if everything goes LED. They will continue to improve lamps for the sole reason that without them, they won't make money any more.
LEDs also have drawbacks as well. The first being they can't run off of AC like a normal lamp, they need DC. This means there will always be some transformer and power loss involved. If the transformer goes bad, your in trouble. Also, if an LED breaks, you will have to completely disassemble the light to fix it and get out the soldering iron. Don't for get heat sinks when soldering these things either, they will be destroyed if you don't. LEDs also cost tons of money right now, and they most likely will continue because there again, lamp companies need to make up for the fact that you will never have to buy a replacement LED.
Also look at the amount of LEDs required to match a lamp. The DLED 36 can't keep up with a 750w S4 ParNel extended life, let along the 300 hour version. I wouldn't be surprised if there are plans for a 1000w HPL to give them another bump up. The lumen output for the extend life would be about 20500 lumen and the non extended version 27375. That is a lot of lumen power. Tungsten also doesn't fade in intensity as it gets older like arc lamps do, well not nearly as noticeably any way.