For one security through obscurity is a thing. Depending on it as your primary "security measure" is stupid on all levels but being part of your security is not a bad thing. Before all someone could get would be your chat history. Other than police, jilted lovers, and state actors no one else gives a crap about that most likely unless you are targeted as an individual. Now by adding access to money that might be accessible via Signal adds more incentive for hackers to not try to hack something else and now make a beeline for Signal. Also it dilutes the efforts of the Signal developers efforts to make a better messaging app. Also crypto in and of itself is questionable, but one that is 85% by one entity waiting to liquidate has been questioned by many organizations as well. The people who own that will expect fair value for it and in essence become billionaires several times over if this really comes to fruition.