So this advisory discussion involved the witnesses proposing not to shoulder any of the burden of the 10%..?

Some witnesses proposed no change to witness rewards including myself for the reasons already stated. To reiterate, witness rewards were already cut 80% in a previous adjustment, one which conducted a reasonable modeling of the minimum safe witness reward structure. The (soon) existence of the SPS does nothing to change that modeling nor does it change a reasonable assessment of the minimum safe witness reward structure. In fact, I would argue based on this sound logic, that if you think the shift from the reward pool of 10% is too high and it should only be 9%, instead of trying to make an unsupported reduction in witness rewards to make up the difference, SPS itself should just be reduced from 10% to 9%. But I personally do not see the need for that all, and I think SPS benefits more from that 10% increase than the rewards pool would benefit from not losing that last 1.5%.

Other witnesses proposed to shift some witness rewards, but ultimately a majority if not supermajority of witnesses were not in favor of that, and not doing so is what the developers (who are also large stakeholders themselves) decided to code.

You are free to view this as unfair self-enrichment or some such, which seems to be the undercurrent of what you are implying even if you don't come out and say it, but I don't. I sincerely believe that nearly if not literally everyone involved on all sides of these issues wants the best for Steem and very few if any witnesses are strongly motivated to maximize their witness rewards beyond what is truly necessary and responsible as a system design. In truth, it just isn't a lot of money for most who are successful investors, business owners, well-paid developers, etc. to even justify the hassles involved, including debates like this one, so we are all must be far more motivated to help make Steem a success, or if not most of us would probably just frankly quit.

In the end, as I said, stakeholders will decide.

I say be proactive and air concerns before it gets to this stage

These exact same concerns were aired several months ago when the SPS was first proposed and developed its funding was discussed. There is very little being brought up now that wasn't already brought up then.

Then, just as now, some suggested that some witness rewards be shifted to cover the cost, and some suggested that witness rewards not be shifted. Some suggested that reward pool be shift, some suggested that SPS be funded only by donations.

What happened more recently is that witnesses and developers had a discussion, considering all of the views that were aired several months ago and since about whether and how SPS should be funded, and the informal consensus that came out discussion was for the 65/15/10/10 split. Ultimately the stakeholders will decide.