I think it is reasonable to assume that libraries provided with the project are being used by external programs. I know one utility which is being used in a rather closed-off community (but nonetheless widely adopted by around 200-300 people), which got broken by this. Their solution is to stay on 3.4 until either 3.6 is fixed or the utility (which probably will be done in this case).
I also think it is the right thinking to allow libraries and more specifically ABI breaks between releases. But those should never occur in a maintenance release, which is what happened here if I got the gist of it. If the break would be between 3.4.x and 3.6.0 it would be fine by me. But breaking between 3.6.0 and 3.6.1 should not happen. I consider this an issue that must be fixed - but the change should most certainly happen with a version beyond 3.6.
And just additionally my 2 cents. Please always consider that although the download rates of Wireshark are mind-blowing and wonderful, the adoption within companies might be even greater with special build versions. There exists many reasons for those versions, be it not enough resources available to bring changes to mainline or having code and adaptations which are for whatever (legal mostly) reasons not able to be publicly available. Changes like these i would see as a risk to those practices, and one of the reasons Wireshark has such a good standing within the community are our policies for long-time stability and maintainability.
Just my own thoughts on this.
cheers
Roland