It would be really nice to have an option in the Ascent Guidance AP for a coasting-free ascent to orbit. I use a bunch of mods like RSS, Engine Ignitor etc. and restarting engines after a coasting phase isn't always possible depending on the engine. As in real life rockets mostly burn as long as orbit isn't achieved yet.
For example: I tried recreating the launch of the SpaceX Falcon 9.1 Orbcomm OG2 launch of July, 14th. The real rocket acheived an 743 x 640 km orbit after 578 seconds of non-stop burning (except the 6 second pause during stage separation). It's impossible to do that with MJ because MJ cuts off the engine as soon as Apoapsis reaches 'Orbit altitude'. With that coasting-free option enabled MJ could change the ascent path to keep the value of Apoapsis constant. Engine cutoff would then be at reaching a circular orbit or - to reference some good ideas in issue #25 - a desired periapsis is reached.

either this is done with PEG or its part of #1061

as i mentioned in a response to issue #404 (you should read that) its not as simple as a checkbox to have everything work - those calculations are very specific to your current ship and it's current cargo tonnage, also not to mention whether or not you have NEAR of ferram installed or any other kind of realistic drag simulator (which mechjeb doesn't truly support yet)

just the information about how long the burn lasts is not enough information to determine the exact launch trajectory they used during that flight for you to efficiently simulate that exact launch (and that direct insertion)... if you can figure out at which kilometer their gravity turn began, the curvature of that turn, and at what altitude the turn finished, THEN, create a world setup that matches earth and our real life planetary system as well as using a realistic fuel and thrust model, and plug all that info into mechjeb and report on the results... you may find its still not achievable... KSP makes too many approximations and shortcuts to make everything work, you're never going to get a realistic real world recreation of a flight down to the exact dV or seconds of burn time...

this is in fact a game and not a simulation...

BUT you can get close with trial and error editing the launch trajectory, but some ships it may just not be possible, too shallow a curve while using a drag simulator will cause you to flip, so you need to wait until you're out of the thickest atmosphere, which prevents direct insertion...

what you are suggesting is possible with mechjeb But its just like skbernard says it need very precise set up of the flight path and thrust amounts

This would be a "Direct Insertion" to orbit. Something I'm referring to in issue #404

This would have an added bonus of saving fuel too, I think. I like it.