Summary

In the interest of ensuring that the developmental playing field between
Bitcoin Unlimited and corporations using its software remains level,
re-license the Bitcoin Unlimited software under the GNU Public License
version 3 (GPLv3) [1] and license new BU code exclusively under GPLv3.

See [3]

Motivation

Recent events have shown that corporations are willing to use BU
software to further their own aims without contributing back to Bitcoin
Unlimited development.

Changing the license from MIT to GPLv3 would at least obligate companies
that distribute derivatives of BU software to provide their modified
source code back to the community.

To quote from [2]:

GPLv3 also provides users with explicit patent protection from the
program’s contributors and redistributors. With GPLv2, users rely on
an implicit patent license to make sure that the company which
provided them a copy won’t sue them, or the people they redistribute
copies to, for patent infringement.*

This patent protection clauses will provide a benefit to BU users
considering the recent increase in patent registrations and patent
litigation threats in the Bitcoin and general blockchain space.

Implementation considerations

Original MIT license clauses need to be preserved, and GPL licensing
clauses added to license existing files under GPL.

All new code contributions would be licensed under GPLv3 or later.

Notes

Since the MIT license restrictions are a subset of the GPL
restrictions, MIT-licensed code can be re-licensed under GPL
provided the original MIT clauses and attributions remain intact.
See [3]
As an example of a project which has re-licensed MIT code under
GPL(v3), see Flowee The Hub. See [4]