Let's get this in perspective: it was only high-level Family mobs that were changed. The Family are a mid-level villain group, and their presence in the higher levels is an aberration in and of itself. They don't even exist at those levels on outdoor maps. They are found in two notable missions, namely one of the TV missions in Grandville and one of Unai Kemen's missions in Peregrine island.
Indoor missions in CoX are inherently resettable, so long as they don't have timers, which these missions don't. That means an endless supply of well-stuffed maps. Furthermore, the high-level Family are so easy to defeat that they're perfect for XP farming, or to give it its more usual name, power leveling.
This change just alters the XP so that it reflects how easy the fights are. What's strange is why it should have taken so long for the Devs to do it; the much loved and soon to be sadly missed TV mission has been around since Issue 7.
We've already looked at the farming phenomenon in CoX. This change is bound to make some farming-positive players react with horror. It's the same sort of thing as we've seen before with portal-summoned Behemoths no longer giving XP and (for those that remember back that far) prisoners getting their XP cut.
There's one other change in Issue 12 that seems - at first glance - to speak directly to power leveling: 'Fixed a long-standing bug with Experience Point and Influence distribution in teams with a large range of levels.' This cryptic note means that typical power leveling teams led by level 50s won't be able to use level 41 characters to lower the team's average level any more, which allowed a broader range of characters to gain XP. However, this change has been explained as a fix to a bug, rather than a nerf.
Having looked over the rest of Issue 12, we're not really seeing any sign of a mass offensive against farmers. The rumors keep flying, but the signs just aren't there. The change to the Family looks much more like a somewhat overdue correction than a stage in a campaign. Even if players miss their TV farms, they can't really argue with the Devs' logic.
So why might the Devs be making this change now, when they could have let sleeping mobsters lie? It's been suggested the change is perhaps due to the forthcoming opportunities for player generated content, about which Positron has said he'll be able to talk more this summer. Unless all the enemy groups are balanced in advance (so the theory goes) so that risk is commensurate with reward, players will just make their own farming missions, packing them full of the most rewarding and least challenging mobs. Pre-nerf high-level Family would have been perfect for this.
All of this seems to say that the Devs don't intend to stop farming, but they aren't going to allow the easiest routes to remain open.