Today PGI announced a couple of unexpected changes that will hit in the next patch, due on Tuesday next week. Firstly they will be implementing a fix so that when you purchase double heat sinks (hereafter DHS) for your mech, the engine sinks get upgraded to DHS as well. Currently they remain singles, and the weight-and-critical-slot-free heatsinks you gain by upgrading to DHS was one of the biggest reasons to cough up the cash for them in the first place. Secondly, they announced that following internal testing they weren't going to be implementing DHS exactly as per tabletop rules. Instead of a DHS being twice as effective as it's single counterpart, it will now be 1.4 times as effective.
This is going to represent the biggest shift that MWO has made from the tabletop rules. Previously PGI have tweaked things here and there, but mostly things that aren't really in tabletop (like LRM flight paths, beam weapon duration and weapon cycle times), or things that aren't so much for game balance but to cope with the networking issues that sixteen giant robots apparently cause for the Crysis engine (like the changes to maximum engine size by class). But this is on a different scale to those changes: this pretty much takes DHS from something you'd buy the second you could afford it to something that won't make a lot of sense to include in an awful lot of mech builds.
Given that a DHS weighs the same as a single but takes up three times the space, their use is going to be really limited. This is probably bad news for trial mechs as well. If any stock builds that use DHS show up in the trial rotation, they're going to be kitted out with weapons that are intended to make full use of the additional efficiency from the original rules and will likely run absurdly hot now.
As well as all that, they announced that the heat for the small laser and all the pulse lasers was being calculated incorrectly and that all of those are going to see increased heat generation from now on. It's important to note that this isn't a nerf of the weapons concerned, just a bug fix that looks like a nerf. Combined with the DHS change, this upcoming patch really isn't looking good for the laser boater, and the small pulse laser is increasingly looking like someone at PGI hates it.
In Brian Eckman's forum post he states the change is due to DHS basically removing heat concerns from the equation in their test environment, meaning we would have wound up seeing nothing but energy boats if they'd left the DHS as they were in tabletop. He's also stated that they're going to monitor the outcome of these changes and adjust the DHS effectiveness accordingly, so this value isn't set in stone.
As it stands, I wouldn't be at all surprised to see DHS use drop off dramatically except for in light and possibly medium mechs, where the effect of "free" double engine heat sinks is a lot more pronounced. Mechs that run without any sinks outside of the engine will get a straight 40% improvement to their heat dissipation now, while those that mount large numbers of single heat sinks will have to consider whether or not they're better off as they are. The change also means that ballistic weapons aren't as dead in the water as they might have been, with weapons that generate low heat looking ever more desirable.
Regardless of its final implementation, the proposed DHS change has unleashed a storm of controversy on the official MWO forums that is unlikely to abate soon.