Centerbrook’s page for its master plan for the Hood suggests that the existing connector to Wilson Hall could be preserved, and it shows the new addition as rising behind the connector.

The addition will obscure most of the front of the Hood Annex, but it will be largely hidden from the Green. In this conceptual plan, at least, the addition is given a signpost in the form of a sort of Joseph Hoffmann ziggurat.

This plan is only a general guide, but it suggests that the preservation of the Wilson Hall entrance is a lost cause. The second and third images on the page show the entire entry below the arch — the stairs, vestibule, door, fenestration, and inscribed granite lintel — demolished and replaced with glazing.

Wilson Hall’s front door will become the Hood Museum’s new principal entry and be transformed by large glass windows to convey transparency and engage passersby on the busy campus green.

A Romanesque building is not the best place to look for transparency… Perhaps a projecting pavilion supporting prominent signage would be just as good, and would also preserve the building’s most distinctive elements. Living with an obtrusive but well-designed entrance and ramp structure outside the building would be a small price to pay to retain the experience of passing through the building’s substantial doorway, with its surfaces of oak, brick, granite, sandstone, and glass.

This master plan led to the Basis for Design for the expansion, and that document will lead to the designs that Williams and Tsien are now beginning. Little more than the general siting of the addition is likely to carry over from the master plan.

More details on that Basis for Design from Art New England (pdf), published a while back:

We intend to go back to the original skin of the building by tearing out the offices and dropped ceiling and returning the Picture Gallery to its original state.

Hood Director Matthew Taylor is referring to Wilson Hall. That link is found in the Hood’s comprehensive page of links about the selection of Williams and Tsien.

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[Update 03.28.2016: Broken code in Hoffman link fixed.]
[Update 01.13.2013: Broken link to Palais Stoclet image replaced with Hoffman link.]