This ADC has an input range of +0.5V to -8V in order to avoid voltage range translation (--> resistor drift). The switches were f.i. MAX319, which is rather slow. The fastest ADC with this range, 1000/s, and up to 160 dB free dynamic range at 0 to 500 Hz applied the HC4053.
It is impressive what can be obtained with the LTC2400. The LTC2400 is a really good ADC, but also has weak points. The switched capacitor technique used here causes current spikes at the input, which can be cumbersome. For instance, I was not able to achieve the datasheet linearity with LTC2440 for 1000/s rate. The latter IC is very sensitive to the input capacitor arrangement, and filtering its supply and reference is complicated. X7R capacitors can cause non-linearity, but you need e.g. 1uF. Is there a good solution for this problem?
The DS-ADC ICs have one fundamental disadvantage: the offset is adjusted to zero as part of the switched capacitor technique. But in this case the correlation between succeeding measurement values is destroyed (kT/C noise). Each measurement is statistically independent from other measurements. If you use a sliding average filter, you get a reduction of noise proportional to 1/sqrt(N).
In contrast, a continuous time Delta-Sigma ADC, as mentioned above, maintains the correlation of succeeding measurements. Simply speaking, if one measurement value was too low, the next one will be too large to compensate this. With a sliding average filter you get a noise reduction proportional to 1/N. This is valid until the inherent 1/f-noise (and drift) destroys this correlation (in my case at about 20s averaging). For ratiometric measurements I measured once <0.03ppm rms noise, which value could be reduced even more today. Continuous time Delta-Sigma ADCs can be constructed so that they have very clean dynamic characteristics. The offset correction has be to established by a circuit or techniques independent on the basic Delta-Sigma activity.
Considering this, it can make sense to develop continuous time DS-ADCs even today. This is the reason why I ponder to start a new development using modern electronics, while there will be no commercial use of it.