Frontiers of LCA knowledge tend to expand while circularity indicators tend to disperse sporadically. Mainly, what some circularity indicators can quantify that LCA does not is monetary value retention. Is the goal of developing new circularity indicators to progress on our comprehension of absolute sustainability assessment? Why wouldn’t they integrate more of current knowledge while LCA does? What's the environmental contribution of quantifying/assessing circularity ?
Regarding the statement of "what some circularity indicators can quantify that LCA does not is monetary value retention", it should be noted that circularity aims at valuing depreciated, used, or degraded products after a second round of use. Contrarily, the LCA is mainly related to the first round of production (or services') offered.
Besides, regarding the argumentation of "Is the goal of developing new circularity indicators to progress on our comprehension of absolute sustainability assessment?", it can be referred that circularity indicators should serve as traceable/monitoring determinants of sustainability assessment. However, such indicators should be better adopted under either the "Analytic hierarchy process (AHP)" or the "Fuzzy Analytic Hierarchy Process". Employing these methods necessitate researchers to design their analysis under diversified criteria of weighted significance.
Moreover, based on the questions of "Why wouldn’t they integrate more of current knowledge while LCA does? What's the environmental contribution of quantifying/assessing circularity ?", it should be argued that LCA is conceptually matching to the traditionally, experimentally former, types of linear economy, whereas circularity can be characterized as a much more versatile and case-specific type of circular economy, under which a more detailed and pluralistic plethora of parameters: economic, environmental, technological, societal, they should be quantified, co-evaluated, verified, and validated.
For instance, one of the aims of CE is to extend the life of the material used. DfD is a good practice that can be linked to this indicator. LCA does not consider the extended life (maybe a series of following cycles) of materials! So quantifying/assessing circularity (e,g, manufacturing process) contributes to the environment such new perspectives while LCA does not!
First I recognize that ISO 14040-44 type LCA may be a limited method to assess circularity. While product category rules (PCR) are important to standardize LCA and allow comparison between products they may be slow to update with the current state of knowledge and society's needs. Given that circularity assessment methods are still in a state of consolidation (e.g., the ISO standards for CE are still under development https://www.iso.org/committee/7203984.html) this is rather normal that standardized LCA and PCR are still limited in providing answers to circularity-type questions.
However, I disagree that LCA as a method cannot assess circularity in a research context. LCA researchers are fond of using a (very) wide range of methods in combination with the basic LCA framework. To name just a few: optimization techniques (multiple-criteria decision analysis, linear programming...), material flow analysis, system dynamics, agent-based modeling, partial and general equilibrium models, input-output analysis, and so on. The reasons are simple: it brings an original methodological contribution (always useful when trying to publish academic articles) and enables the researchers to apply LCA to a more difficult question/product system to analyze (say a fleet of vehicles (https://pubs.acs.org/doi/abs/10.1021/es5060868?casa_token=uJ0zllzDrL8AAAAA:UcvFPy8NI7kDSnrXEnSF2mvSP90tGRFbKXCfPcZJzJzeuBiOvSyoDWt7BfSa08D1rWSFS-gImEHKiPJg)) than what a standardized LCA would allow. Therefore, with appropriate goal & scope and functional unit definitions (see the still very relevant 1999 report from Goedkoop et al. on product-service systems https://simapro.com/wp-content/uploads/2016/05/Product-Service-Systems-main-report.pdf) and the use of appropriate methods to complement LCA, I can't see why LCA would not be able to assess the environmental performance of any CE strategies (but I remain open to being clearly demonstrated why not!)
Second, regarding CE indicators I will just repeat what I understood from the excellent article by Boyer et al. (Article Three‐dimensional product circularity
) as I quite agree with their proposition. In the same way that sustainability assessment should include economic, social, and environmental aspects, circularity assessment should include three dimensions: recirculation, utilization, endurance. According to the authors, developing indicators around these dimensions would provide enough flexibility to adapt to specific product systems and enough standardization and transparency to enable product comparison. I think such standardized indicators in those three dimensions could complement existing LCA-based environmental product declarations (EPD) (in the same way that french EPDs (FDEP) include additional information on indoor air quality and water and soil pollution).In the end, I think new standards and PCR need to be developed to i) define how CE systems should be assessed (with an emphasis on the goal & scope and functional unit definitions), ii) define what CE indicators should be used to assess the three dimensions of circularity for the particular product system.