i think the fort save will still be significant well into the game.
The first reason i think this is the presumption that magic items that boost save will be infrequent in modern style low magic campaigns.
The second reason is that the save bonuses are lower for the basic classes. The advanced classes come close to DND levels, but only the specialized ones seem to get to the normal save.
The third reason is that it seems in a modern setting there will not be the focus on one stat... multiple stats are required for even general efficiency, far fewer "i am a cha 6 and i like it" dump stats that wont hurt all that much. So overall, the stats will be more spread out, producing lower bonuses. Psionics also seem to favor spreading stats around since each power has its own stat.
Now, the house rule i am considering is not to increase the DC and increase the likelihood of PC being killed or taken out of the fight. Instead, i want to discourage taking the risk.
I am considering making a MADE MD save result in a STUNNED FOR 1 ROUND. So, if you fail your MD save, you are at -1 hp and basically out. if you make your MD save, you are stunned for 1 round. Thus its never a good bet to say " i can make the MD save and i got tons of HP so i will rush into the machine gun and..." because the probablye result is to LOSE and action and be stuck out in the open.
temporary losses of action seems to me to lead to better more dramatic scenes than increasing the probability of near death experiences. being hung out where you might soon be hit, or might soon recover, is a tense few moments. being Koed and knowing you are out for the fight, is not as tense.
IMX