While it may be realistic for UserApp, it doesn't take much to make it difficult, complex or even impossible. There have been similar discussions on HN at least a couple of times. The first that comes to mind is the release of the DOOM3 engine source code by id Tech / Carmack[1]
On a personal level I can see the excuse of saying "screw license, we'll just email the source to our customers and what they choose to do is up to them", but there may be unlicened changes in dependencies.
While some ideas fail, some of those are carried on to new ideas, and you may have written code as part of the failed startup, which would be a significant IP to you, and might be an integrated part of your next idea's success.
Yes, the latter comment is not very "open source" minded, but given how many projects start out as proprietary (or at least partially), it is a scenario one should keep in mind.
So overall, the intention is good, and can work for some projects, but you never know what the future brings (which, ironically, is why you draft pledges like this.
Thanks for your willingness to take responsibility and I hope you'll go the distance.
[1] https://twitter.com/ID_AA_Carmack/statuses/13661445988720230...