Looks like work will start on Phase 1 work to:
design and construct a multi-use trail that extends from the existing Mountains-to-Sound Trail ending at the Jose Rizal Bridge, move west along the south side of I-90 and then moving south along I-5 to Holgate Bridge.
SDOT goes on to announce that they've awarded the construction contract, and that work is expected to run from June to September, 2011:
The Washington State Department of Transportation is managing the construction of the Mountains-to-Sound Trail and has now awarded the work to Tri-State Construction. The construction work is expected to begin in June, 2011, when the weather is dryer, and wrap up sometime in September, 2011.
Phase 2 will cross I-5 and provide a critical link between Airport and the I-90 trail. For more information, see the project page.