Ah, from http://www.alwaystouchout.com/project/43

Initially, TfL may substitute the current trains running the Euston -
Watford service (aged Class 313 and Class 508 trains) with some
(modified) stock cascaded from the Victoria line after that line
receives its new trains. The Victoria line stock is similar to the
Bakerloo line fleet, and the two could be merged fairly easily later
on (see below).

Services would continue to operate as now (6tph Bakerloo and 3tph
Watford DC) but Watford DC trains would be longer (six or seven cars).

Bakerloo Line (re-)extension
TfL eventually plan to re-extend the Bakerloo line from Harrow &
Wealdstone to Watford Junction, replacing the Watford DC services
between Watford Junction and Euston. Bakerloo line services would run
every 10 minutes to Watford, an improvement on the current 20-minute
frequency to Euston. [TfL: T2025 report]

Kilburn High Road and South Hampstead would cease to be served by
direct trains to central London, but would gain services to Camden and
Stratford as part of the proposed Queen\'s Park to Stratford service,
which would run every 15 minutes.

The cost savings from cutting the Silverlink service to Euston would
be used to fund capacity improvements for the North London Line.