An idea to mix deflection rated I Joists?
I doubt you’d notice the difference in deflection walking from L/360 to L/600. 

When we design floor systems, we use the “critical span” to size the joists. That is to say, spans (from bearing wall to bearing wall) are seldom identical. So, we size the joists for the critical span and then use the same size joists throughout (so the floor sheathing is at the same height). The shorter spans will have a “stiffer” system, but it’s not noticeable. 

If you’ve ever walked across a “stiff” floor system and then a “spongy” floor system, it’s noticeable. But if you walk across a stiff floor system and a “really stiff” floor system, it’s not noticeable. 

So, if you mix the grade of the I-Joists, I doubt you’d notice by walking from one to another. However, if the joists are not “stiff” enough, (L/600) the tile will crack, of course. 

An alternative to mixing grades, is to mix spacings of the I-Joists. I do not like joists spaced further than 16” o.c. for FLOOR systems. Perhaps you could space the joists at 12” o.c. for tile and 16” o.c. for wood and carpet areas. 

BTW, the main reason we use L/360 is to keep the gypsum board ceilings below from cracking. Anything less, (i.e.: L/240, etc.) you’re asking for trouble...it will crack the plaster ceiling when fully loaded....(when you have your birthday party and everyone is in the same room.)

Also, we add 1 or 2 floor joists under the refrigerator and the freezer...making the spacing 8” o.c. 

(Also, we try to determine if the client will have waterbeds.)