Halliday & Matthiessen (2014: 484):
With concession, there is a special hypotactic construction that may be used when the β-clause is an attributive relational one: the Attribute is given the status of marked Theme and the Rheme begins with as or though — an item which would be the structural Theme in the unmarked case (as in tempting as it may be; little though it may be).
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A work that makes considerable use of this construction is Alan Bennett's The Uncommon Reader.