So, I should start out by saying that I have read the other threads in which Celtavian is making their case against Rogues.
I disagree with him on several points, but they have already been stated by others in those threads, and there is no point in trying to convince Celtavian that the existing rogue is a perfectly functional class.
I do acknowledge that with Celtavian's DMing style, and the preferences of his group (which seems highly combat focused and melee combat in particular), the rogue may seem lacking. So my thoughts here are specifically for rogue modifications for your group, rather than something I think is needed for the class in general.
Making some rogue-specific abilities into feats does seem like a valid way to have other characters in your group. Trapfinding is an excellent candidate for this, but you may just want to allow any character with Disable device to find and disable magical traps.
The rogue would still have 1/2 levels bonus to perception and disable device skills related to traps, as well as trap sense and the trap spotter rogue talent.
This is similar to the evolution of Tracking. In 3.5 it was a feat that used the survival skill, and rangers got for free as the 'Best Trackers'. Now it is a normal function of the survival skill, but rangers get a number of extra tracking benefits denied to other classes to give them the advantage.
Regarding beefing up the Rogue class, I would not suggest upping their Fort save. Thematically, they're still lightly armoured, mobile characters. Since your group is into melee offense, just flat out give the rogue full BAB and a d10 hit die.
In keeping with this, rather than the Assassin's accuracy, I would suggest something like the duelist's precise strike ability. If your group finds it difficult to position themselves for sneak attack, then change the conditions so that they are not position-dependent.
The Precise strike ability will offer less potential bonus damage than sneak attacks, but the rogue won't be dependent on the positioning of other characters, or use of Feinting to activate it.
A similar option could be provided for rogues focusing on ranged combat.
If you did make them a full BAB, it would probably make sense to scale back the skill points to 6/level or 4/level. They can still have a good range, but they'll be more about combat, and less about skill-based troubleshooting.
Aside: A friend of mine has allowed a rogue with a full BAB in his campaign before with positive results. In this case, it was a Pathfinder-updated War of the Burning Sky campaign. However, in this case, the group had only 3 players (a ranger, a rogue and an oracle) and were at substantial tactical disadvantage because of their small numbers. So, it was not a case of the player being lured to this rogue by this bonus.
This only represented a change to that rogue in particular, and did not affect NPCs. To address their lack of any arcane ability, the ranger was granted access to the sorcerer spell list with the bard's casting progression. I believe the oracle was modified in some way as well, but I do not recall the specifics.
(Okay, so I got around to this earlier than I thought)