It's more than just adding the Tazer to the belt. I can say from experience that carrying all that crap can SUCK. Hip and lower back problems are rampant. We started issuing suspenders to guys to pull some of the weight off the hips and distribute it better across the body. A lot of Deptments are looking at vests to get gear off the belts but still accessible. Then try running in that crap. I like the vest idea. Actually you'll notice that the $1M cost is offset by an expected $1M a YEAR savings in workman's comp claims.
Then you run into the basic real estate on the belt. A pistol, radio, and handcuffs can cover most of the belt. Then you add latex gloves and a CPR mask for BSI protection, baton, extra magazines, and a cell phone there isn't much room left. My daughter isn't a cop but she uses a duty belt to shoot USPSA Production (first time this weekend, but that's another thread) and her waist is so small the holster and four mags cover 80% of the belt. She wouldn't have room for handcuffs if you replace the second set of mags with the radio.
Ask Modesto (CA) Sheriffs Dept about adding a Tazer to a duty belt. The original policy didn't specify how the Tazer should be located on the officer. They had an unruly suspect trying to kick out the door of a patrol car and a female officer went for her Tazer and grabbed her Glock instead. That's part of the readon the newer Tazers aren't shaped anything like a traditional pistol grip. The new guidance is the Tazer SHALL be on the opposite side of the officer than the pistol or on a thigh holster.
Putting a duty weapon on the thigh vice the Tazer I personaly see as a problem. For years officers have been trained to go for the belt if the need the wepon, bascically the opposite of Modesto is a possibility. Officer goes for where the pistol used to be and get the Tazer then get shot or stabbed. Muscle memory is a double edged sword. I am much faster from the belt than a thigh rig because that is what I normally use. I only use a thigh holster when I'm also purposely using a long gun 90% of the time. If I didn't plan on the long gun I use a belt holster.