Interesting idea and with proper planning, it is definitely feasible in certain areas. One would have to take a hard look at how long the patrol can sustain without burn-out plus keep patrols within artillery range (or priority for CAS/AWT) and within CASEVAC range.

If they're going in covertly for recon (digging in), then I'd recommend a max duration of 72 hours. After that, brains are fried.

How long should tour length be in this scenario? I'd probably think 6-9 months.
This is where I tend to agree with Bill on his arguments about risk aversion (I think it was one of your points, right? ). I can understand being inside a reasonable envelop for casevac support, but when we look at a force-on-force comparison, I cannot recall too many open-source reports of attacks on patrolling elements (perhaps a few times in Ramadi and then some occasions in Afghanistan) where the enemy had us outmatched in terms of shooters and "firepower". Why then do we have to keep them within range of indirect fire? I agree that it is a good objective to try to meet, but we should not let that limit us. Attach one or two gun trucks for mobile fires platforms, or motorize at least one 60mm tube, crew, and ammo supply (METT-T dependent) and I think you've got the support fires you might need.

The conditions are the key here. I am currently thinking along Afghanistan lines, where things are sufficiently open that LOS is decent. If we are looking at an urban environment, the situation is so thoroughly different that even if combat outposts were inkspotted throughout the city, the force density still needs to be very high if we want to achieve the constant number of forces afield that slapout mentions.

We can do this, with the right approach, indefinitely. I've seen it done (albeit with mechanized scouts aboard LAVs), for essentially four months, with only two 4-day reset periods. Our trains were on the move constantly, pushing supplies and recovery downed vehicles back to the CSS node for repair. This was in northern Iraq, during a tough winter. Do troops get sick and injured? Absolutely, but those are the costs that we need to manage, as leaders, the best we can.