I personally think its a good idea, I wouldent want to wait a additional 6 years to play a good game agian. My only concern is that the source engine may age to fast before they get to episode 3 (Take a look at Crysis). Note, they never said no Half Life 4...
On a side note:
"Finally, Newell also warned fans not to expect a Half-Life movie anytime soon, as he had some unkind words to say about the script treatments Hollywood has offered: "They all sucked!"
*Edit* Hmm, seems there are other threads pertaining to this issue, my mistake.