Refleks said:

The B-2 definitely needs replacing but I don't like the idea of giving up range or payload which is presumably the case (though not necessarily) with a smaller aircraft

I agree, I don't like the reduction in payload.

Although how much payload is actually reduced is the question. And whether overall munitions capacity is dictated more by weight, or by how many hardpoints there are on the internal rotary rack launchers? It's possible the B21 could carry say a comparable number of SDB or 500lb bombs to the B2 due to hardpoints, but lack the overall weight capacity of the B2 to say carry 2x 30,000lb MOP bunker busters.

In terms of range, the (totally speculative) discussion I've read so far believes the B21 may have a longer overall range then the B2 due to having 2x fuel efficient engines as opposed to the 4x of the B2. 

Best picture to date:

And a look at the makings of:

https://time.com/6238168/b-21-raider-bomber-us-military-exclusive/

From the Time article, one of the less sexy but most important aspects of the B21 is that its designed to be much lower maintenance than the B2 due to improvements in the design as well as more modern RAM coatings.

Meanwhile, despite the B21s ascension, the B52 shall remain eternal. Perhaps the 2nd longest running weapon system of the US after the M2 Browning .50