A combination of all these approaches is not only possible, but practical and scientifically plausible (though I tend to hate enemies having auto-aim, it's like they're using tab-targeting and we're not.)
Weapons that lock-on and track targets should be nothing new or disturbing; we have those already. The reason they make sense within a game is that we have measures to fight them when they're launched, either by shooting them down, forcing them to lose track by skillful dodging, or flares/ECM to confuse their tracking. As long as multiple countermeasures and counterplay exist, lock-ons are perfectly fair and explainable.
Telegraphs for attacks are a muddier topic to me, because it's very easy to cross the line between "scientifically accurate" and "easy mode." I can understand if there's equipment available that gives us the OPTION of having extra telegraphs for enemy attacks or other predictions; it allows a sort of training wheel that lets us practice dodging a particularly troublesome type of attack. Otherwise, the sounds and sights of enemy behaviors should be up to us to track; having a boss always call out "I'M DROPPIN MAH MORTARS RIIIIIIGHT HERE!" for example, will quickly become patronizing and brainless, but hearing a distinctive CLUNK of a mortar tube getting set up, followed by the resounding "FOOMP" of the shell firing should be all the cue we need to look up, estimate a trajectory, and GET THE HELL OUT OF THE WAY. Having a giant red circle painted on the ground overlay removes any need to pay attention to the enemy's actions.
Now, if we only GET that red circle BY paying attention and giving our computers early visual data with which to produce that circle, possibly broadcasting it to our team? THAT'S a different story...
Imagine that for a second; a recon frame equipped with tracking software that relies on the pilot's direct observation, causing his computer to generate advanced warning in the forms of audio-visual telegraphs for his squad! Part of his job will be to keep key enemies in sight at all times so his computer can share targeting and incoming data with his team! It could even be a toggled option for squadmates who want the extra info or those who find it distracting. The equipment would of course take up space in your build, of course. Not only will some teams distinctly appreciate it, but it allows the devs to put it much more dangerous and subtle enemy behaviors, knowing that players have a way to counter that subtlety. It's cause and effect, player choice, build tradeoffs AND a potentially useful gameplay role! Now THAT'S what I call reconnaissance!