The HMCAD1511 is a nice chip, however pretty darn expensive, for just a 10 or 20 MHz frontend. For 8 channels, you would need also 2 of them.
For the simple lowMHz DSO a dedicated VGA and ADC may become cheaper. Although, with 2pcs HMCAD1511, the whole thing may look much simpler on the PCB.
If it'd be me and cheaping out on some project cobbling for fun, I'd opt for external voltage controlled VGA such as AD8330 from the far east sources ($2-3 a pop) and a 100MSps ADC, such as AD9288 (also dirt cheap from far east), four times. Leaving me at about $30 for the whole VGA+ADC saga. Of course this does not likely make much if any sense for a commercial design, at least I won't be quite worried about damaging a $70 IC in the process.
There may be even cheaper possibility than AD8330, as a DC to 20MHz or so VGA, this is still a bit overkill.
And also, I've never worked with LVDS on an FPGA, hence a lot of parallel buses from the smaller ADCs are more familiar to me as to what I can do
