Eventually open source licence

Would it be possible to write a legally valid eventually open source licence? Such a licence would include a commited date at the point of publication of when the code would be released open source. It could potentially require users of the licence to submit source code into escrow to be released at that date.

The licence would balance the commercial needs of making return on investment, whilst making a reputation-maintaining commitment to the community, and also future-proofing such that users software is not locked into unsupported closed-source formats.