People (including aspiring, and occasionally experienced, woodworkers) can look at this sort of thing and assume the rear joints1 just can't take the stress, but you can actually make chairs with this basic design if you build them right.
although desk only holds a hutch at back (over most supported area), a tower computer also toward the back but along one side, and a keyboard toward front. So not front loaded with weight at all, except for actual table top
There's an important additional weight you aren't factoring in and that's the weight of your arms when the desk is in use. Unless you sit in such a way that your fingers perch above the keyboard and don't press upon the desktop at all the amount of pressure exerted by your arms is significant enough that you don't want to ignore it2.
And if you intend to write on the desk occasionally a good portion of the weight of your torso will press upon the desktop without you realising it..... and far more towards the front edge than the centre.
Plus, as covered in the Comments, for safety you have to overbuild for the accidental or unthinking overloading situation — someone tripping and putting a hand on the edge of the desk to steady themselves, leaning against it, or worse, actually sitting on it.
So how to build it right
Two options are using bridle joints (open mortise-and-tenon joints) or finger joints.
For additional strength and to future-proof it you should probably lock the joint with pegs. Additional reinforcement may make the pegs redundant but they look good and don't take much time to do so I'd personally add them anyway.
Since you've indicated you're open to using external fixturing (e.g. truss plates) or a diagonal support of some kind by all means add something. They'll add so much to the overall strength and stiffness. Have a look at the various iterations of the ZigZag Chair designed by Gerrit Rietveld to get other ideas of how you might reinforce the joints.
You haven't mentioned what wood you intend or hope to use here so a word about that is in order. If you're using hardwood you can use thinner stock than softwood, much thinner for the stronger hardwoods; as a very rough indicator, with oak you can use stock half the dimensions of pine, for equivalent strength.
Be selective in the pieces you use. You don't want any knots or significant grain runout (grain that angles sharply across) on the vertical members in particular. As much as possible these pieces should be straight-grained and free from defects.
I don't think I'll include front horizontal cross pieces in design, but might add to back.
Yes I don't think this adds anything of structural necessity, unless the top is fair thin and the legs are spaced widely apart.
choose a wider rather than narrower leg design to increase the surface area of the joint
The surface area of the joint is an important consideration, but bear in mind the axis of the strain. If you used e.g. 1"x3" (25mm x 76mm) stock you maximise the beam strength if they are edge-on to the sitter and desktop compared to the opposite. If you prefer the flat look you might want to go quite wide, and/or consider adding a third leg.
1 From responses I've read most seem to focus on the top-rear joint as the one that will experience the most stress. But I think you have works out to 60:40 top to bottom you still don't want to skimp on the bottom joint. And if you're using power tools to create the joinery you actually save time doing the two joints the same because there's no additional setup time.
2 You only tend to notice this when you use something like a cheesy flatpack computer desk with a pull-out keyboard tray! If you haven't ever used one of those believe me, you want to factor that in.
