Ta-da! You've just invented POL supply! Congratulations. :)
I believe this is how chipsets on the motherboards are powered for the past 10 years or so. Providing you can make/buy DC-DC stable enough for your application Figure 2 is good way to go.
Now, the feedback from your sensors makes me worried. I think digital connection will be much more precise and reliable. Ideally with differential protocol. For example, if your sensor chip has I2C interface you can use something like AN11075 to send it over RS-485 more than 1 km away without any loss of precision.
Here is a ready-made product you might find interesting. It extends I2C up to 300m and.. wait for it... it already has DC-DC on board. Therer are other modules over there, some feeding power into the line, others using it to power themselves.
As you can see, they support true bus architecture, with one Boost module providing power and data link to multiple Buck modules. You can put it in the box with micro-controller, add several (again, ready-made) DAC modules and then write simple program that interrogates sensors and puts their output to DACs in a loop. This is actually one evening project, come to think of it. For the cost of under $300 per 10 sensors.
UPDATE: Here is an illustration of possible system configuration:
DACs: you can use individual modules, like MCP4725, or go crazy with 16 channel ADAU1966A monster (cost is not an issue, right? ;) )
MCU: Arduino, Raspberry or whatever you feel more comfortable with
Boost module: The one I linked before or any other ready-made I2C-to-differential converter.
Buck module: The complementary device to above or a combination of DC-DC module + I2C-to-differential converter.
Amplifier: ADC with I2C interface and desired resolution, like ADS1115. Or better yet, the link that you provided mentions an option for I2C output straight from the sensor. That would simplify things a lot.